1config ARCH 2 string 3 option env="ARCH" 4 5config KERNELVERSION 6 string 7 option env="KERNELVERSION" 8 9config DEFCONFIG_LIST 10 string 11 depends on !UML 12 option defconfig_list 13 default "/lib/modules/$UNAME_RELEASE/.config" 14 default "/etc/kernel-config" 15 default "/boot/config-$UNAME_RELEASE" 16 default "$ARCH_DEFCONFIG" 17 default "arch/$ARCH/defconfig" 18 19config CONSTRUCTORS 20 bool 21 depends on !UML 22 23config IRQ_WORK 24 bool 25 26config BUILDTIME_EXTABLE_SORT 27 bool 28 29menu "General setup" 30 31config BROKEN 32 bool 33 34config BROKEN_ON_SMP 35 bool 36 depends on BROKEN || !SMP 37 default y 38 39config INIT_ENV_ARG_LIMIT 40 int 41 default 32 if !UML 42 default 128 if UML 43 help 44 Maximum of each of the number of arguments and environment 45 variables passed to init from the kernel command line. 46 47 48config CROSS_COMPILE 49 string "Cross-compiler tool prefix" 50 help 51 Same as running 'make CROSS_COMPILE=prefix-' but stored for 52 default make runs in this kernel build directory. You don't 53 need to set this unless you want the configured kernel build 54 directory to select the cross-compiler automatically. 55 56config COMPILE_TEST 57 bool "Compile also drivers which will not load" 58 default n 59 help 60 Some drivers can be compiled on a different platform than they are 61 intended to be run on. Despite they cannot be loaded there (or even 62 when they load they cannot be used due to missing HW support), 63 developers still, opposing to distributors, might want to build such 64 drivers to compile-test them. 65 66 If you are a developer and want to build everything available, say Y 67 here. If you are a user/distributor, say N here to exclude useless 68 drivers to be distributed. 69 70config LOCALVERSION 71 string "Local version - append to kernel release" 72 help 73 Append an extra string to the end of your kernel version. 74 This will show up when you type uname, for example. 75 The string you set here will be appended after the contents of 76 any files with a filename matching localversion* in your 77 object and source tree, in that order. Your total string can 78 be a maximum of 64 characters. 79 80config LOCALVERSION_AUTO 81 bool "Automatically append version information to the version string" 82 default y 83 help 84 This will try to automatically determine if the current tree is a 85 release tree by looking for git tags that belong to the current 86 top of tree revision. 87 88 A string of the format -gxxxxxxxx will be added to the localversion 89 if a git-based tree is found. The string generated by this will be 90 appended after any matching localversion* files, and after the value 91 set in CONFIG_LOCALVERSION. 92 93 (The actual string used here is the first eight characters produced 94 by running the command: 95 96 $ git rev-parse --verify HEAD 97 98 which is done within the script "scripts/setlocalversion".) 99 100config HAVE_KERNEL_GZIP 101 bool 102 103config HAVE_KERNEL_BZIP2 104 bool 105 106config HAVE_KERNEL_LZMA 107 bool 108 109config HAVE_KERNEL_XZ 110 bool 111 112config HAVE_KERNEL_LZO 113 bool 114 115config HAVE_KERNEL_LZ4 116 bool 117 118choice 119 prompt "Kernel compression mode" 120 default KERNEL_GZIP 121 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 122 help 123 The linux kernel is a kind of self-extracting executable. 124 Several compression algorithms are available, which differ 125 in efficiency, compression and decompression speed. 126 Compression speed is only relevant when building a kernel. 127 Decompression speed is relevant at each boot. 128 129 If you have any problems with bzip2 or lzma compressed 130 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older 131 version of this functionality (bzip2 only), for 2.4, was 132 supplied by Christian Ludwig) 133 134 High compression options are mostly useful for users, who 135 are low on disk space (embedded systems), but for whom ram 136 size matters less. 137 138 If in doubt, select 'gzip' 139 140config KERNEL_GZIP 141 bool "Gzip" 142 depends on HAVE_KERNEL_GZIP 143 help 144 The old and tried gzip compression. It provides a good balance 145 between compression ratio and decompression speed. 146 147config KERNEL_BZIP2 148 bool "Bzip2" 149 depends on HAVE_KERNEL_BZIP2 150 help 151 Its compression ratio and speed is intermediate. 152 Decompression speed is slowest among the choices. The kernel 153 size is about 10% smaller with bzip2, in comparison to gzip. 154 Bzip2 uses a large amount of memory. For modern kernels you 155 will need at least 8MB RAM or more for booting. 156 157config KERNEL_LZMA 158 bool "LZMA" 159 depends on HAVE_KERNEL_LZMA 160 help 161 This compression algorithm's ratio is best. Decompression speed 162 is between gzip and bzip2. Compression is slowest. 163 The kernel size is about 33% smaller with LZMA in comparison to gzip. 164 165config KERNEL_XZ 166 bool "XZ" 167 depends on HAVE_KERNEL_XZ 168 help 169 XZ uses the LZMA2 algorithm and instruction set specific 170 BCJ filters which can improve compression ratio of executable 171 code. The size of the kernel is about 30% smaller with XZ in 172 comparison to gzip. On architectures for which there is a BCJ 173 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ 174 will create a few percent smaller kernel than plain LZMA. 175 176 The speed is about the same as with LZMA: The decompression 177 speed of XZ is better than that of bzip2 but worse than gzip 178 and LZO. Compression is slow. 179 180config KERNEL_LZO 181 bool "LZO" 182 depends on HAVE_KERNEL_LZO 183 help 184 Its compression ratio is the poorest among the choices. The kernel 185 size is about 10% bigger than gzip; however its speed 186 (both compression and decompression) is the fastest. 187 188config KERNEL_LZ4 189 bool "LZ4" 190 depends on HAVE_KERNEL_LZ4 191 help 192 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding. 193 A preliminary version of LZ4 de/compression tool is available at 194 <https://code.google.com/p/lz4/>. 195 196 Its compression ratio is worse than LZO. The size of the kernel 197 is about 8% bigger than LZO. But the decompression speed is 198 faster than LZO. 199 200endchoice 201 202config DEFAULT_HOSTNAME 203 string "Default hostname" 204 default "(none)" 205 help 206 This option determines the default system hostname before userspace 207 calls sethostname(2). The kernel traditionally uses "(none)" here, 208 but you may wish to use a different default here to make a minimal 209 system more usable with less configuration. 210 211config SWAP 212 bool "Support for paging of anonymous memory (swap)" 213 depends on MMU && BLOCK 214 default y 215 help 216 This option allows you to choose whether you want to have support 217 for so called swap devices or swap files in your kernel that are 218 used to provide more virtual memory than the actual RAM present 219 in your computer. If unsure say Y. 220 221config SYSVIPC 222 bool "System V IPC" 223 ---help--- 224 Inter Process Communication is a suite of library functions and 225 system calls which let processes (running programs) synchronize and 226 exchange information. It is generally considered to be a good thing, 227 and some programs won't run unless you say Y here. In particular, if 228 you want to run the DOS emulator dosemu under Linux (read the 229 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>), 230 you'll need to say Y here. 231 232 You can find documentation about IPC with "info ipc" and also in 233 section 6.4 of the Linux Programmer's Guide, available from 234 <http://www.tldp.org/guides.html>. 235 236config SYSVIPC_SYSCTL 237 bool 238 depends on SYSVIPC 239 depends on SYSCTL 240 default y 241 242config POSIX_MQUEUE 243 bool "POSIX Message Queues" 244 depends on NET 245 ---help--- 246 POSIX variant of message queues is a part of IPC. In POSIX message 247 queues every message has a priority which decides about succession 248 of receiving it by a process. If you want to compile and run 249 programs written e.g. for Solaris with use of its POSIX message 250 queues (functions mq_*) say Y here. 251 252 POSIX message queues are visible as a filesystem called 'mqueue' 253 and can be mounted somewhere if you want to do filesystem 254 operations on message queues. 255 256 If unsure, say Y. 257 258config POSIX_MQUEUE_SYSCTL 259 bool 260 depends on POSIX_MQUEUE 261 depends on SYSCTL 262 default y 263 264config CROSS_MEMORY_ATTACH 265 bool "Enable process_vm_readv/writev syscalls" 266 depends on MMU 267 default y 268 help 269 Enabling this option adds the system calls process_vm_readv and 270 process_vm_writev which allow a process with the correct privileges 271 to directly read from or write to another process' address space. 272 See the man page for more details. 273 274config FHANDLE 275 bool "open by fhandle syscalls" if EXPERT 276 select EXPORTFS 277 default y 278 help 279 If you say Y here, a user level program will be able to map 280 file names to handle and then later use the handle for 281 different file system operations. This is useful in implementing 282 userspace file servers, which now track files using handles instead 283 of names. The handle would remain the same even if file names 284 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2) 285 syscalls. 286 287config USELIB 288 bool "uselib syscall" 289 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION 290 help 291 This option enables the uselib syscall, a system call used in the 292 dynamic linker from libc5 and earlier. glibc does not use this 293 system call. If you intend to run programs built on libc5 or 294 earlier, you may need to enable this syscall. Current systems 295 running glibc can safely disable this. 296 297config AUDIT 298 bool "Auditing support" 299 depends on NET 300 help 301 Enable auditing infrastructure that can be used with another 302 kernel subsystem, such as SELinux (which requires this for 303 logging of avc messages output). System call auditing is included 304 on architectures which support it. 305 306config HAVE_ARCH_AUDITSYSCALL 307 bool 308 309config AUDITSYSCALL 310 def_bool y 311 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL 312 313config AUDIT_WATCH 314 def_bool y 315 depends on AUDITSYSCALL 316 select FSNOTIFY 317 318config AUDIT_TREE 319 def_bool y 320 depends on AUDITSYSCALL 321 select FSNOTIFY 322 323source "kernel/irq/Kconfig" 324source "kernel/time/Kconfig" 325 326menu "CPU/Task time and stats accounting" 327 328config VIRT_CPU_ACCOUNTING 329 bool 330 331choice 332 prompt "Cputime accounting" 333 default TICK_CPU_ACCOUNTING if !PPC64 334 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64 335 336# Kind of a stub config for the pure tick based cputime accounting 337config TICK_CPU_ACCOUNTING 338 bool "Simple tick based cputime accounting" 339 depends on !S390 && !NO_HZ_FULL 340 help 341 This is the basic tick based cputime accounting that maintains 342 statistics about user, system and idle time spent on per jiffies 343 granularity. 344 345 If unsure, say Y. 346 347config VIRT_CPU_ACCOUNTING_NATIVE 348 bool "Deterministic task and CPU time accounting" 349 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL 350 select VIRT_CPU_ACCOUNTING 351 help 352 Select this option to enable more accurate task and CPU time 353 accounting. This is done by reading a CPU counter on each 354 kernel entry and exit and on transitions within the kernel 355 between system, softirq and hardirq state, so there is a 356 small performance impact. In the case of s390 or IBM POWER > 5, 357 this also enables accounting of stolen time on logically-partitioned 358 systems. 359 360config VIRT_CPU_ACCOUNTING_GEN 361 bool "Full dynticks CPU time accounting" 362 depends on HAVE_CONTEXT_TRACKING 363 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 364 select VIRT_CPU_ACCOUNTING 365 select CONTEXT_TRACKING 366 help 367 Select this option to enable task and CPU time accounting on full 368 dynticks systems. This accounting is implemented by watching every 369 kernel-user boundaries using the context tracking subsystem. 370 The accounting is thus performed at the expense of some significant 371 overhead. 372 373 For now this is only useful if you are working on the full 374 dynticks subsystem development. 375 376 If unsure, say N. 377 378config IRQ_TIME_ACCOUNTING 379 bool "Fine granularity task level IRQ time accounting" 380 depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL 381 help 382 Select this option to enable fine granularity task irq time 383 accounting. This is done by reading a timestamp on each 384 transitions between softirq and hardirq state, so there can be a 385 small performance impact. 386 387 If in doubt, say N here. 388 389endchoice 390 391config BSD_PROCESS_ACCT 392 bool "BSD Process Accounting" 393 depends on MULTIUSER 394 help 395 If you say Y here, a user level program will be able to instruct the 396 kernel (via a special system call) to write process accounting 397 information to a file: whenever a process exits, information about 398 that process will be appended to the file by the kernel. The 399 information includes things such as creation time, owning user, 400 command name, memory usage, controlling terminal etc. (the complete 401 list is in the struct acct in <file:include/linux/acct.h>). It is 402 up to the user level program to do useful things with this 403 information. This is generally a good idea, so say Y. 404 405config BSD_PROCESS_ACCT_V3 406 bool "BSD Process Accounting version 3 file format" 407 depends on BSD_PROCESS_ACCT 408 default n 409 help 410 If you say Y here, the process accounting information is written 411 in a new file format that also logs the process IDs of each 412 process and it's parent. Note that this file format is incompatible 413 with previous v0/v1/v2 file formats, so you will need updated tools 414 for processing it. A preliminary version of these tools is available 415 at <http://www.gnu.org/software/acct/>. 416 417config TASKSTATS 418 bool "Export task/process statistics through netlink" 419 depends on NET 420 depends on MULTIUSER 421 default n 422 help 423 Export selected statistics for tasks/processes through the 424 generic netlink interface. Unlike BSD process accounting, the 425 statistics are available during the lifetime of tasks/processes as 426 responses to commands. Like BSD accounting, they are sent to user 427 space on task exit. 428 429 Say N if unsure. 430 431config TASK_DELAY_ACCT 432 bool "Enable per-task delay accounting" 433 depends on TASKSTATS 434 select SCHED_INFO 435 help 436 Collect information on time spent by a task waiting for system 437 resources like cpu, synchronous block I/O completion and swapping 438 in pages. Such statistics can help in setting a task's priorities 439 relative to other tasks for cpu, io, rss limits etc. 440 441 Say N if unsure. 442 443config TASK_XACCT 444 bool "Enable extended accounting over taskstats" 445 depends on TASKSTATS 446 help 447 Collect extended task accounting data and send the data 448 to userland for processing over the taskstats interface. 449 450 Say N if unsure. 451 452config TASK_IO_ACCOUNTING 453 bool "Enable per-task storage I/O accounting" 454 depends on TASK_XACCT 455 help 456 Collect information on the number of bytes of storage I/O which this 457 task has caused. 458 459 Say N if unsure. 460 461endmenu # "CPU/Task time and stats accounting" 462 463menu "RCU Subsystem" 464 465config TREE_RCU 466 bool 467 default y if !PREEMPT && SMP 468 help 469 This option selects the RCU implementation that is 470 designed for very large SMP system with hundreds or 471 thousands of CPUs. It also scales down nicely to 472 smaller systems. 473 474config PREEMPT_RCU 475 bool 476 default y if PREEMPT 477 help 478 This option selects the RCU implementation that is 479 designed for very large SMP systems with hundreds or 480 thousands of CPUs, but for which real-time response 481 is also required. It also scales down nicely to 482 smaller systems. 483 484 Select this option if you are unsure. 485 486config TINY_RCU 487 bool 488 default y if !PREEMPT && !SMP 489 help 490 This option selects the RCU implementation that is 491 designed for UP systems from which real-time response 492 is not required. This option greatly reduces the 493 memory footprint of RCU. 494 495config RCU_EXPERT 496 bool "Make expert-level adjustments to RCU configuration" 497 default n 498 help 499 This option needs to be enabled if you wish to make 500 expert-level adjustments to RCU configuration. By default, 501 no such adjustments can be made, which has the often-beneficial 502 side-effect of preventing "make oldconfig" from asking you all 503 sorts of detailed questions about how you would like numerous 504 obscure RCU options to be set up. 505 506 Say Y if you need to make expert-level adjustments to RCU. 507 508 Say N if you are unsure. 509 510config SRCU 511 bool 512 help 513 This option selects the sleepable version of RCU. This version 514 permits arbitrary sleeping or blocking within RCU read-side critical 515 sections. 516 517config TASKS_RCU 518 bool 519 default n 520 select SRCU 521 help 522 This option enables a task-based RCU implementation that uses 523 only voluntary context switch (not preemption!), idle, and 524 user-mode execution as quiescent states. 525 526config RCU_STALL_COMMON 527 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE ) 528 help 529 This option enables RCU CPU stall code that is common between 530 the TINY and TREE variants of RCU. The purpose is to allow 531 the tiny variants to disable RCU CPU stall warnings, while 532 making these warnings mandatory for the tree variants. 533 534config CONTEXT_TRACKING 535 bool 536 537config CONTEXT_TRACKING_FORCE 538 bool "Force context tracking" 539 depends on CONTEXT_TRACKING 540 default y if !NO_HZ_FULL 541 help 542 The major pre-requirement for full dynticks to work is to 543 support the context tracking subsystem. But there are also 544 other dependencies to provide in order to make the full 545 dynticks working. 546 547 This option stands for testing when an arch implements the 548 context tracking backend but doesn't yet fullfill all the 549 requirements to make the full dynticks feature working. 550 Without the full dynticks, there is no way to test the support 551 for context tracking and the subsystems that rely on it: RCU 552 userspace extended quiescent state and tickless cputime 553 accounting. This option copes with the absence of the full 554 dynticks subsystem by forcing the context tracking on all 555 CPUs in the system. 556 557 Say Y only if you're working on the development of an 558 architecture backend for the context tracking. 559 560 Say N otherwise, this option brings an overhead that you 561 don't want in production. 562 563 564config RCU_FANOUT 565 int "Tree-based hierarchical RCU fanout value" 566 range 2 64 if 64BIT 567 range 2 32 if !64BIT 568 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT 569 default 64 if 64BIT 570 default 32 if !64BIT 571 help 572 This option controls the fanout of hierarchical implementations 573 of RCU, allowing RCU to work efficiently on machines with 574 large numbers of CPUs. This value must be at least the fourth 575 root of NR_CPUS, which allows NR_CPUS to be insanely large. 576 The default value of RCU_FANOUT should be used for production 577 systems, but if you are stress-testing the RCU implementation 578 itself, small RCU_FANOUT values allow you to test large-system 579 code paths on small(er) systems. 580 581 Select a specific number if testing RCU itself. 582 Take the default if unsure. 583 584config RCU_FANOUT_LEAF 585 int "Tree-based hierarchical RCU leaf-level fanout value" 586 range 2 64 if 64BIT 587 range 2 32 if !64BIT 588 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT 589 default 16 590 help 591 This option controls the leaf-level fanout of hierarchical 592 implementations of RCU, and allows trading off cache misses 593 against lock contention. Systems that synchronize their 594 scheduling-clock interrupts for energy-efficiency reasons will 595 want the default because the smaller leaf-level fanout keeps 596 lock contention levels acceptably low. Very large systems 597 (hundreds or thousands of CPUs) will instead want to set this 598 value to the maximum value possible in order to reduce the 599 number of cache misses incurred during RCU's grace-period 600 initialization. These systems tend to run CPU-bound, and thus 601 are not helped by synchronized interrupts, and thus tend to 602 skew them, which reduces lock contention enough that large 603 leaf-level fanouts work well. 604 605 Select a specific number if testing RCU itself. 606 607 Select the maximum permissible value for large systems. 608 609 Take the default if unsure. 610 611config RCU_FAST_NO_HZ 612 bool "Accelerate last non-dyntick-idle CPU's grace periods" 613 depends on NO_HZ_COMMON && SMP && RCU_EXPERT 614 default n 615 help 616 This option permits CPUs to enter dynticks-idle state even if 617 they have RCU callbacks queued, and prevents RCU from waking 618 these CPUs up more than roughly once every four jiffies (by 619 default, you can adjust this using the rcutree.rcu_idle_gp_delay 620 parameter), thus improving energy efficiency. On the other 621 hand, this option increases the duration of RCU grace periods, 622 for example, slowing down synchronize_rcu(). 623 624 Say Y if energy efficiency is critically important, and you 625 don't care about increased grace-period durations. 626 627 Say N if you are unsure. 628 629config TREE_RCU_TRACE 630 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU ) 631 select DEBUG_FS 632 help 633 This option provides tracing for the TREE_RCU and 634 PREEMPT_RCU implementations, permitting Makefile to 635 trivially select kernel/rcutree_trace.c. 636 637config RCU_BOOST 638 bool "Enable RCU priority boosting" 639 depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT 640 default n 641 help 642 This option boosts the priority of preempted RCU readers that 643 block the current preemptible RCU grace period for too long. 644 This option also prevents heavy loads from blocking RCU 645 callback invocation for all flavors of RCU. 646 647 Say Y here if you are working with real-time apps or heavy loads 648 Say N here if you are unsure. 649 650config RCU_KTHREAD_PRIO 651 int "Real-time priority to use for RCU worker threads" 652 range 1 99 if RCU_BOOST 653 range 0 99 if !RCU_BOOST 654 default 1 if RCU_BOOST 655 default 0 if !RCU_BOOST 656 depends on RCU_EXPERT 657 help 658 This option specifies the SCHED_FIFO priority value that will be 659 assigned to the rcuc/n and rcub/n threads and is also the value 660 used for RCU_BOOST (if enabled). If you are working with a 661 real-time application that has one or more CPU-bound threads 662 running at a real-time priority level, you should set 663 RCU_KTHREAD_PRIO to a priority higher than the highest-priority 664 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO 665 value of 1 is appropriate in the common case, which is real-time 666 applications that do not have any CPU-bound threads. 667 668 Some real-time applications might not have a single real-time 669 thread that saturates a given CPU, but instead might have 670 multiple real-time threads that, taken together, fully utilize 671 that CPU. In this case, you should set RCU_KTHREAD_PRIO to 672 a priority higher than the lowest-priority thread that is 673 conspiring to prevent the CPU from running any non-real-time 674 tasks. For example, if one thread at priority 10 and another 675 thread at priority 5 are between themselves fully consuming 676 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be 677 set to priority 6 or higher. 678 679 Specify the real-time priority, or take the default if unsure. 680 681config RCU_BOOST_DELAY 682 int "Milliseconds to delay boosting after RCU grace-period start" 683 range 0 3000 684 depends on RCU_BOOST 685 default 500 686 help 687 This option specifies the time to wait after the beginning of 688 a given grace period before priority-boosting preempted RCU 689 readers blocking that grace period. Note that any RCU reader 690 blocking an expedited RCU grace period is boosted immediately. 691 692 Accept the default if unsure. 693 694config RCU_NOCB_CPU 695 bool "Offload RCU callback processing from boot-selected CPUs" 696 depends on TREE_RCU || PREEMPT_RCU 697 depends on RCU_EXPERT || NO_HZ_FULL 698 default n 699 help 700 Use this option to reduce OS jitter for aggressive HPC or 701 real-time workloads. It can also be used to offload RCU 702 callback invocation to energy-efficient CPUs in battery-powered 703 asymmetric multiprocessors. 704 705 This option offloads callback invocation from the set of 706 CPUs specified at boot time by the rcu_nocbs parameter. 707 For each such CPU, a kthread ("rcuox/N") will be created to 708 invoke callbacks, where the "N" is the CPU being offloaded, 709 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and 710 "s" for RCU-sched. Nothing prevents this kthread from running 711 on the specified CPUs, but (1) the kthreads may be preempted 712 between each callback, and (2) affinity or cgroups can be used 713 to force the kthreads to run on whatever set of CPUs is desired. 714 715 Say Y here if you want to help to debug reduced OS jitter. 716 Say N here if you are unsure. 717 718choice 719 prompt "Build-forced no-CBs CPUs" 720 default RCU_NOCB_CPU_NONE 721 depends on RCU_NOCB_CPU 722 help 723 This option allows no-CBs CPUs (whose RCU callbacks are invoked 724 from kthreads rather than from softirq context) to be specified 725 at build time. Additional no-CBs CPUs may be specified by 726 the rcu_nocbs= boot parameter. 727 728config RCU_NOCB_CPU_NONE 729 bool "No build_forced no-CBs CPUs" 730 help 731 This option does not force any of the CPUs to be no-CBs CPUs. 732 Only CPUs designated by the rcu_nocbs= boot parameter will be 733 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU 734 kthreads whose names begin with "rcuo". All other CPUs will 735 invoke their own RCU callbacks in softirq context. 736 737 Select this option if you want to choose no-CBs CPUs at 738 boot time, for example, to allow testing of different no-CBs 739 configurations without having to rebuild the kernel each time. 740 741config RCU_NOCB_CPU_ZERO 742 bool "CPU 0 is a build_forced no-CBs CPU" 743 help 744 This option forces CPU 0 to be a no-CBs CPU, so that its RCU 745 callbacks are invoked by a per-CPU kthread whose name begins 746 with "rcuo". Additional CPUs may be designated as no-CBs 747 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs. 748 All other CPUs will invoke their own RCU callbacks in softirq 749 context. 750 751 Select this if CPU 0 needs to be a no-CBs CPU for real-time 752 or energy-efficiency reasons, but the real reason it exists 753 is to ensure that randconfig testing covers mixed systems. 754 755config RCU_NOCB_CPU_ALL 756 bool "All CPUs are build_forced no-CBs CPUs" 757 help 758 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs= 759 boot parameter will be ignored. All CPUs' RCU callbacks will 760 be executed in the context of per-CPU rcuo kthreads created for 761 this purpose. Assuming that the kthreads whose names start with 762 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter 763 on the remaining CPUs, but might decrease memory locality during 764 RCU-callback invocation, thus potentially degrading throughput. 765 766 Select this if all CPUs need to be no-CBs CPUs for real-time 767 or energy-efficiency reasons. 768 769endchoice 770 771config RCU_EXPEDITE_BOOT 772 bool 773 default n 774 help 775 This option enables expedited grace periods at boot time, 776 as if rcu_expedite_gp() had been invoked early in boot. 777 The corresponding rcu_unexpedite_gp() is invoked from 778 rcu_end_inkernel_boot(), which is intended to be invoked 779 at the end of the kernel-only boot sequence, just before 780 init is exec'ed. 781 782 Accept the default if unsure. 783 784endmenu # "RCU Subsystem" 785 786config BUILD_BIN2C 787 bool 788 default n 789 790config IKCONFIG 791 tristate "Kernel .config support" 792 select BUILD_BIN2C 793 ---help--- 794 This option enables the complete Linux kernel ".config" file 795 contents to be saved in the kernel. It provides documentation 796 of which kernel options are used in a running kernel or in an 797 on-disk kernel. This information can be extracted from the kernel 798 image file with the script scripts/extract-ikconfig and used as 799 input to rebuild the current kernel or to build another kernel. 800 It can also be extracted from a running kernel by reading 801 /proc/config.gz if enabled (below). 802 803config IKCONFIG_PROC 804 bool "Enable access to .config through /proc/config.gz" 805 depends on IKCONFIG && PROC_FS 806 ---help--- 807 This option enables access to the kernel configuration file 808 through /proc/config.gz. 809 810config LOG_BUF_SHIFT 811 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)" 812 range 12 25 813 default 17 814 depends on PRINTK 815 help 816 Select the minimal kernel log buffer size as a power of 2. 817 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config 818 parameter, see below. Any higher size also might be forced 819 by "log_buf_len" boot parameter. 820 821 Examples: 822 17 => 128 KB 823 16 => 64 KB 824 15 => 32 KB 825 14 => 16 KB 826 13 => 8 KB 827 12 => 4 KB 828 829config LOG_CPU_MAX_BUF_SHIFT 830 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)" 831 depends on SMP 832 range 0 21 833 default 12 if !BASE_SMALL 834 default 0 if BASE_SMALL 835 depends on PRINTK 836 help 837 This option allows to increase the default ring buffer size 838 according to the number of CPUs. The value defines the contribution 839 of each CPU as a power of 2. The used space is typically only few 840 lines however it might be much more when problems are reported, 841 e.g. backtraces. 842 843 The increased size means that a new buffer has to be allocated and 844 the original static one is unused. It makes sense only on systems 845 with more CPUs. Therefore this value is used only when the sum of 846 contributions is greater than the half of the default kernel ring 847 buffer as defined by LOG_BUF_SHIFT. The default values are set 848 so that more than 64 CPUs are needed to trigger the allocation. 849 850 Also this option is ignored when "log_buf_len" kernel parameter is 851 used as it forces an exact (power of two) size of the ring buffer. 852 853 The number of possible CPUs is used for this computation ignoring 854 hotplugging making the compuation optimal for the the worst case 855 scenerio while allowing a simple algorithm to be used from bootup. 856 857 Examples shift values and their meaning: 858 17 => 128 KB for each CPU 859 16 => 64 KB for each CPU 860 15 => 32 KB for each CPU 861 14 => 16 KB for each CPU 862 13 => 8 KB for each CPU 863 12 => 4 KB for each CPU 864 865config NMI_LOG_BUF_SHIFT 866 int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)" 867 range 10 21 868 default 13 869 depends on PRINTK_NMI 870 help 871 Select the size of a per-CPU buffer where NMI messages are temporary 872 stored. They are copied to the main log buffer in a safe context 873 to avoid a deadlock. The value defines the size as a power of 2. 874 875 NMI messages are rare and limited. The largest one is when 876 a backtrace is printed. It usually fits into 4KB. Select 877 8KB if you want to be on the safe side. 878 879 Examples: 880 17 => 128 KB for each CPU 881 16 => 64 KB for each CPU 882 15 => 32 KB for each CPU 883 14 => 16 KB for each CPU 884 13 => 8 KB for each CPU 885 12 => 4 KB for each CPU 886 887# 888# Architectures with an unreliable sched_clock() should select this: 889# 890config HAVE_UNSTABLE_SCHED_CLOCK 891 bool 892 893config GENERIC_SCHED_CLOCK 894 bool 895 896# 897# For architectures that want to enable the support for NUMA-affine scheduler 898# balancing logic: 899# 900config ARCH_SUPPORTS_NUMA_BALANCING 901 bool 902 903# 904# For architectures that prefer to flush all TLBs after a number of pages 905# are unmapped instead of sending one IPI per page to flush. The architecture 906# must provide guarantees on what happens if a clean TLB cache entry is 907# written after the unmap. Details are in mm/rmap.c near the check for 908# should_defer_flush. The architecture should also consider if the full flush 909# and the refill costs are offset by the savings of sending fewer IPIs. 910config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH 911 bool 912 913# 914# For architectures that know their GCC __int128 support is sound 915# 916config ARCH_SUPPORTS_INT128 917 bool 918 919# For architectures that (ab)use NUMA to represent different memory regions 920# all cpu-local but of different latencies, such as SuperH. 921# 922config ARCH_WANT_NUMA_VARIABLE_LOCALITY 923 bool 924 925config NUMA_BALANCING 926 bool "Memory placement aware NUMA scheduler" 927 depends on ARCH_SUPPORTS_NUMA_BALANCING 928 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY 929 depends on SMP && NUMA && MIGRATION 930 help 931 This option adds support for automatic NUMA aware memory/task placement. 932 The mechanism is quite primitive and is based on migrating memory when 933 it has references to the node the task is running on. 934 935 This system will be inactive on UMA systems. 936 937config NUMA_BALANCING_DEFAULT_ENABLED 938 bool "Automatically enable NUMA aware memory/task placement" 939 default y 940 depends on NUMA_BALANCING 941 help 942 If set, automatic NUMA balancing will be enabled if running on a NUMA 943 machine. 944 945menuconfig CGROUPS 946 bool "Control Group support" 947 select KERNFS 948 help 949 This option adds support for grouping sets of processes together, for 950 use with process control subsystems such as Cpusets, CFS, memory 951 controls or device isolation. 952 See 953 - Documentation/scheduler/sched-design-CFS.txt (CFS) 954 - Documentation/cgroups/ (features for grouping, isolation 955 and resource control) 956 957 Say N if unsure. 958 959if CGROUPS 960 961config PAGE_COUNTER 962 bool 963 964config MEMCG 965 bool "Memory controller" 966 select PAGE_COUNTER 967 select EVENTFD 968 help 969 Provides control over the memory footprint of tasks in a cgroup. 970 971config MEMCG_SWAP 972 bool "Swap controller" 973 depends on MEMCG && SWAP 974 help 975 Provides control over the swap space consumed by tasks in a cgroup. 976 977config MEMCG_SWAP_ENABLED 978 bool "Swap controller enabled by default" 979 depends on MEMCG_SWAP 980 default y 981 help 982 Memory Resource Controller Swap Extension comes with its price in 983 a bigger memory consumption. General purpose distribution kernels 984 which want to enable the feature but keep it disabled by default 985 and let the user enable it by swapaccount=1 boot command line 986 parameter should have this option unselected. 987 For those who want to have the feature enabled by default should 988 select this option (if, for some reason, they need to disable it 989 then swapaccount=0 does the trick). 990 991config BLK_CGROUP 992 bool "IO controller" 993 depends on BLOCK 994 default n 995 ---help--- 996 Generic block IO controller cgroup interface. This is the common 997 cgroup interface which should be used by various IO controlling 998 policies. 999 1000 Currently, CFQ IO scheduler uses it to recognize task groups and 1001 control disk bandwidth allocation (proportional time slice allocation) 1002 to such task groups. It is also used by bio throttling logic in 1003 block layer to implement upper limit in IO rates on a device. 1004 1005 This option only enables generic Block IO controller infrastructure. 1006 One needs to also enable actual IO controlling logic/policy. For 1007 enabling proportional weight division of disk bandwidth in CFQ, set 1008 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set 1009 CONFIG_BLK_DEV_THROTTLING=y. 1010 1011 See Documentation/cgroups/blkio-controller.txt for more information. 1012 1013config DEBUG_BLK_CGROUP 1014 bool "IO controller debugging" 1015 depends on BLK_CGROUP 1016 default n 1017 ---help--- 1018 Enable some debugging help. Currently it exports additional stat 1019 files in a cgroup which can be useful for debugging. 1020 1021config CGROUP_WRITEBACK 1022 bool 1023 depends on MEMCG && BLK_CGROUP 1024 default y 1025 1026menuconfig CGROUP_SCHED 1027 bool "CPU controller" 1028 default n 1029 help 1030 This feature lets CPU scheduler recognize task groups and control CPU 1031 bandwidth allocation to such task groups. It uses cgroups to group 1032 tasks. 1033 1034if CGROUP_SCHED 1035config FAIR_GROUP_SCHED 1036 bool "Group scheduling for SCHED_OTHER" 1037 depends on CGROUP_SCHED 1038 default CGROUP_SCHED 1039 1040config CFS_BANDWIDTH 1041 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED" 1042 depends on FAIR_GROUP_SCHED 1043 default n 1044 help 1045 This option allows users to define CPU bandwidth rates (limits) for 1046 tasks running within the fair group scheduler. Groups with no limit 1047 set are considered to be unconstrained and will run with no 1048 restriction. 1049 See tip/Documentation/scheduler/sched-bwc.txt for more information. 1050 1051config RT_GROUP_SCHED 1052 bool "Group scheduling for SCHED_RR/FIFO" 1053 depends on CGROUP_SCHED 1054 default n 1055 help 1056 This feature lets you explicitly allocate real CPU bandwidth 1057 to task groups. If enabled, it will also make it impossible to 1058 schedule realtime tasks for non-root users until you allocate 1059 realtime bandwidth for them. 1060 See Documentation/scheduler/sched-rt-group.txt for more information. 1061 1062endif #CGROUP_SCHED 1063 1064config CGROUP_PIDS 1065 bool "PIDs controller" 1066 help 1067 Provides enforcement of process number limits in the scope of a 1068 cgroup. Any attempt to fork more processes than is allowed in the 1069 cgroup will fail. PIDs are fundamentally a global resource because it 1070 is fairly trivial to reach PID exhaustion before you reach even a 1071 conservative kmemcg limit. As a result, it is possible to grind a 1072 system to halt without being limited by other cgroup policies. The 1073 PIDs controller is designed to stop this from happening. 1074 1075 It should be noted that organisational operations (such as attaching 1076 to a cgroup hierarchy will *not* be blocked by the PIDs controller), 1077 since the PIDs limit only affects a process's ability to fork, not to 1078 attach to a cgroup. 1079 1080config CGROUP_FREEZER 1081 bool "Freezer controller" 1082 help 1083 Provides a way to freeze and unfreeze all tasks in a 1084 cgroup. 1085 1086 This option affects the ORIGINAL cgroup interface. The cgroup2 memory 1087 controller includes important in-kernel memory consumers per default. 1088 1089 If you're using cgroup2, say N. 1090 1091config CGROUP_HUGETLB 1092 bool "HugeTLB controller" 1093 depends on HUGETLB_PAGE 1094 select PAGE_COUNTER 1095 default n 1096 help 1097 Provides a cgroup controller for HugeTLB pages. 1098 When you enable this, you can put a per cgroup limit on HugeTLB usage. 1099 The limit is enforced during page fault. Since HugeTLB doesn't 1100 support page reclaim, enforcing the limit at page fault time implies 1101 that, the application will get SIGBUS signal if it tries to access 1102 HugeTLB pages beyond its limit. This requires the application to know 1103 beforehand how much HugeTLB pages it would require for its use. The 1104 control group is tracked in the third page lru pointer. This means 1105 that we cannot use the controller with huge page less than 3 pages. 1106 1107config CPUSETS 1108 bool "Cpuset controller" 1109 help 1110 This option will let you create and manage CPUSETs which 1111 allow dynamically partitioning a system into sets of CPUs and 1112 Memory Nodes and assigning tasks to run only within those sets. 1113 This is primarily useful on large SMP or NUMA systems. 1114 1115 Say N if unsure. 1116 1117config PROC_PID_CPUSET 1118 bool "Include legacy /proc/<pid>/cpuset file" 1119 depends on CPUSETS 1120 default y 1121 1122config CGROUP_DEVICE 1123 bool "Device controller" 1124 help 1125 Provides a cgroup controller implementing whitelists for 1126 devices which a process in the cgroup can mknod or open. 1127 1128config CGROUP_CPUACCT 1129 bool "Simple CPU accounting controller" 1130 help 1131 Provides a simple controller for monitoring the 1132 total CPU consumed by the tasks in a cgroup. 1133 1134config CGROUP_PERF 1135 bool "Perf controller" 1136 depends on PERF_EVENTS 1137 help 1138 This option extends the perf per-cpu mode to restrict monitoring 1139 to threads which belong to the cgroup specified and run on the 1140 designated cpu. 1141 1142 Say N if unsure. 1143 1144config CGROUP_DEBUG 1145 bool "Example controller" 1146 default n 1147 help 1148 This option enables a simple controller that exports 1149 debugging information about the cgroups framework. 1150 1151 Say N. 1152 1153endif # CGROUPS 1154 1155config CHECKPOINT_RESTORE 1156 bool "Checkpoint/restore support" if EXPERT 1157 select PROC_CHILDREN 1158 default n 1159 help 1160 Enables additional kernel features in a sake of checkpoint/restore. 1161 In particular it adds auxiliary prctl codes to setup process text, 1162 data and heap segment sizes, and a few additional /proc filesystem 1163 entries. 1164 1165 If unsure, say N here. 1166 1167menuconfig NAMESPACES 1168 bool "Namespaces support" if EXPERT 1169 depends on MULTIUSER 1170 default !EXPERT 1171 help 1172 Provides the way to make tasks work with different objects using 1173 the same id. For example same IPC id may refer to different objects 1174 or same user id or pid may refer to different tasks when used in 1175 different namespaces. 1176 1177if NAMESPACES 1178 1179config UTS_NS 1180 bool "UTS namespace" 1181 default y 1182 help 1183 In this namespace tasks see different info provided with the 1184 uname() system call 1185 1186config IPC_NS 1187 bool "IPC namespace" 1188 depends on (SYSVIPC || POSIX_MQUEUE) 1189 default y 1190 help 1191 In this namespace tasks work with IPC ids which correspond to 1192 different IPC objects in different namespaces. 1193 1194config USER_NS 1195 bool "User namespace" 1196 default n 1197 help 1198 This allows containers, i.e. vservers, to use user namespaces 1199 to provide different user info for different servers. 1200 1201 When user namespaces are enabled in the kernel it is 1202 recommended that the MEMCG option also be enabled and that 1203 user-space use the memory control groups to limit the amount 1204 of memory a memory unprivileged users can use. 1205 1206 If unsure, say N. 1207 1208config PID_NS 1209 bool "PID Namespaces" 1210 default y 1211 help 1212 Support process id namespaces. This allows having multiple 1213 processes with the same pid as long as they are in different 1214 pid namespaces. This is a building block of containers. 1215 1216config NET_NS 1217 bool "Network namespace" 1218 depends on NET 1219 default y 1220 help 1221 Allow user space to create what appear to be multiple instances 1222 of the network stack. 1223 1224endif # NAMESPACES 1225 1226config SCHED_AUTOGROUP 1227 bool "Automatic process group scheduling" 1228 select CGROUPS 1229 select CGROUP_SCHED 1230 select FAIR_GROUP_SCHED 1231 help 1232 This option optimizes the scheduler for common desktop workloads by 1233 automatically creating and populating task groups. This separation 1234 of workloads isolates aggressive CPU burners (like build jobs) from 1235 desktop applications. Task group autogeneration is currently based 1236 upon task session. 1237 1238config SYSFS_DEPRECATED 1239 bool "Enable deprecated sysfs features to support old userspace tools" 1240 depends on SYSFS 1241 default n 1242 help 1243 This option adds code that switches the layout of the "block" class 1244 devices, to not show up in /sys/class/block/, but only in 1245 /sys/block/. 1246 1247 This switch is only active when the sysfs.deprecated=1 boot option is 1248 passed or the SYSFS_DEPRECATED_V2 option is set. 1249 1250 This option allows new kernels to run on old distributions and tools, 1251 which might get confused by /sys/class/block/. Since 2007/2008 all 1252 major distributions and tools handle this just fine. 1253 1254 Recent distributions and userspace tools after 2009/2010 depend on 1255 the existence of /sys/class/block/, and will not work with this 1256 option enabled. 1257 1258 Only if you are using a new kernel on an old distribution, you might 1259 need to say Y here. 1260 1261config SYSFS_DEPRECATED_V2 1262 bool "Enable deprecated sysfs features by default" 1263 default n 1264 depends on SYSFS 1265 depends on SYSFS_DEPRECATED 1266 help 1267 Enable deprecated sysfs by default. 1268 1269 See the CONFIG_SYSFS_DEPRECATED option for more details about this 1270 option. 1271 1272 Only if you are using a new kernel on an old distribution, you might 1273 need to say Y here. Even then, odds are you would not need it 1274 enabled, you can always pass the boot option if absolutely necessary. 1275 1276config RELAY 1277 bool "Kernel->user space relay support (formerly relayfs)" 1278 help 1279 This option enables support for relay interface support in 1280 certain file systems (such as debugfs). 1281 It is designed to provide an efficient mechanism for tools and 1282 facilities to relay large amounts of data from kernel space to 1283 user space. 1284 1285 If unsure, say N. 1286 1287config BLK_DEV_INITRD 1288 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support" 1289 depends on BROKEN || !FRV 1290 help 1291 The initial RAM filesystem is a ramfs which is loaded by the 1292 boot loader (loadlin or lilo) and that is mounted as root 1293 before the normal boot procedure. It is typically used to 1294 load modules needed to mount the "real" root file system, 1295 etc. See <file:Documentation/initrd.txt> for details. 1296 1297 If RAM disk support (BLK_DEV_RAM) is also included, this 1298 also enables initial RAM disk (initrd) support and adds 1299 15 Kbytes (more on some other architectures) to the kernel size. 1300 1301 If unsure say Y. 1302 1303if BLK_DEV_INITRD 1304 1305source "usr/Kconfig" 1306 1307endif 1308 1309choice 1310 prompt "Compiler optimization level" 1311 default CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE 1312 1313config CC_OPTIMIZE_FOR_PERFORMANCE 1314 bool "Optimize for performance" 1315 help 1316 This is the default optimization level for the kernel, building 1317 with the "-O2" compiler flag for best performance and most 1318 helpful compile-time warnings. 1319 1320config CC_OPTIMIZE_FOR_SIZE 1321 bool "Optimize for size" 1322 help 1323 Enabling this option will pass "-Os" instead of "-O2" to 1324 your compiler resulting in a smaller kernel. 1325 1326 If unsure, say N. 1327 1328endchoice 1329 1330config SYSCTL 1331 bool 1332 1333config ANON_INODES 1334 bool 1335 1336config HAVE_UID16 1337 bool 1338 1339config SYSCTL_EXCEPTION_TRACE 1340 bool 1341 help 1342 Enable support for /proc/sys/debug/exception-trace. 1343 1344config SYSCTL_ARCH_UNALIGN_NO_WARN 1345 bool 1346 help 1347 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap 1348 Allows arch to define/use @no_unaligned_warning to possibly warn 1349 about unaligned access emulation going on under the hood. 1350 1351config SYSCTL_ARCH_UNALIGN_ALLOW 1352 bool 1353 help 1354 Enable support for /proc/sys/kernel/unaligned-trap 1355 Allows arches to define/use @unaligned_enabled to runtime toggle 1356 the unaligned access emulation. 1357 see arch/parisc/kernel/unaligned.c for reference 1358 1359config HAVE_PCSPKR_PLATFORM 1360 bool 1361 1362# interpreter that classic socket filters depend on 1363config BPF 1364 bool 1365 1366menuconfig EXPERT 1367 bool "Configure standard kernel features (expert users)" 1368 # Unhide debug options, to make the on-by-default options visible 1369 select DEBUG_KERNEL 1370 help 1371 This option allows certain base kernel options and settings 1372 to be disabled or tweaked. This is for specialized 1373 environments which can tolerate a "non-standard" kernel. 1374 Only use this if you really know what you are doing. 1375 1376config UID16 1377 bool "Enable 16-bit UID system calls" if EXPERT 1378 depends on HAVE_UID16 && MULTIUSER 1379 default y 1380 help 1381 This enables the legacy 16-bit UID syscall wrappers. 1382 1383config MULTIUSER 1384 bool "Multiple users, groups and capabilities support" if EXPERT 1385 default y 1386 help 1387 This option enables support for non-root users, groups and 1388 capabilities. 1389 1390 If you say N here, all processes will run with UID 0, GID 0, and all 1391 possible capabilities. Saying N here also compiles out support for 1392 system calls related to UIDs, GIDs, and capabilities, such as setuid, 1393 setgid, and capset. 1394 1395 If unsure, say Y here. 1396 1397config SGETMASK_SYSCALL 1398 bool "sgetmask/ssetmask syscalls support" if EXPERT 1399 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH 1400 ---help--- 1401 sys_sgetmask and sys_ssetmask are obsolete system calls 1402 no longer supported in libc but still enabled by default in some 1403 architectures. 1404 1405 If unsure, leave the default option here. 1406 1407config SYSFS_SYSCALL 1408 bool "Sysfs syscall support" if EXPERT 1409 default y 1410 ---help--- 1411 sys_sysfs is an obsolete system call no longer supported in libc. 1412 Note that disabling this option is more secure but might break 1413 compatibility with some systems. 1414 1415 If unsure say Y here. 1416 1417config SYSCTL_SYSCALL 1418 bool "Sysctl syscall support" if EXPERT 1419 depends on PROC_SYSCTL 1420 default n 1421 select SYSCTL 1422 ---help--- 1423 sys_sysctl uses binary paths that have been found challenging 1424 to properly maintain and use. The interface in /proc/sys 1425 using paths with ascii names is now the primary path to this 1426 information. 1427 1428 Almost nothing using the binary sysctl interface so if you are 1429 trying to save some space it is probably safe to disable this, 1430 making your kernel marginally smaller. 1431 1432 If unsure say N here. 1433 1434config KALLSYMS 1435 bool "Load all symbols for debugging/ksymoops" if EXPERT 1436 default y 1437 help 1438 Say Y here to let the kernel print out symbolic crash information and 1439 symbolic stack backtraces. This increases the size of the kernel 1440 somewhat, as all symbols have to be loaded into the kernel image. 1441 1442config KALLSYMS_ALL 1443 bool "Include all symbols in kallsyms" 1444 depends on DEBUG_KERNEL && KALLSYMS 1445 help 1446 Normally kallsyms only contains the symbols of functions for nicer 1447 OOPS messages and backtraces (i.e., symbols from the text and inittext 1448 sections). This is sufficient for most cases. And only in very rare 1449 cases (e.g., when a debugger is used) all symbols are required (e.g., 1450 names of variables from the data sections, etc). 1451 1452 This option makes sure that all symbols are loaded into the kernel 1453 image (i.e., symbols from all sections) in cost of increased kernel 1454 size (depending on the kernel configuration, it may be 300KiB or 1455 something like this). 1456 1457 Say N unless you really need all symbols. 1458 1459config KALLSYMS_ABSOLUTE_PERCPU 1460 bool 1461 default X86_64 && SMP 1462 1463config KALLSYMS_BASE_RELATIVE 1464 bool 1465 depends on KALLSYMS 1466 default !IA64 && !(TILE && 64BIT) 1467 help 1468 Instead of emitting them as absolute values in the native word size, 1469 emit the symbol references in the kallsyms table as 32-bit entries, 1470 each containing a relative value in the range [base, base + U32_MAX] 1471 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either 1472 an absolute value in the range [0, S32_MAX] or a relative value in the 1473 range [base, base + S32_MAX], where base is the lowest relative symbol 1474 address encountered in the image. 1475 1476 On 64-bit builds, this reduces the size of the address table by 50%, 1477 but more importantly, it results in entries whose values are build 1478 time constants, and no relocation pass is required at runtime to fix 1479 up the entries based on the runtime load address of the kernel. 1480 1481config PRINTK 1482 default y 1483 bool "Enable support for printk" if EXPERT 1484 select IRQ_WORK 1485 help 1486 This option enables normal printk support. Removing it 1487 eliminates most of the message strings from the kernel image 1488 and makes the kernel more or less silent. As this makes it 1489 very difficult to diagnose system problems, saying N here is 1490 strongly discouraged. 1491 1492config PRINTK_NMI 1493 def_bool y 1494 depends on PRINTK 1495 depends on HAVE_NMI 1496 1497config BUG 1498 bool "BUG() support" if EXPERT 1499 default y 1500 help 1501 Disabling this option eliminates support for BUG and WARN, reducing 1502 the size of your kernel image and potentially quietly ignoring 1503 numerous fatal conditions. You should only consider disabling this 1504 option for embedded systems with no facilities for reporting errors. 1505 Just say Y. 1506 1507config ELF_CORE 1508 depends on COREDUMP 1509 default y 1510 bool "Enable ELF core dumps" if EXPERT 1511 help 1512 Enable support for generating core dumps. Disabling saves about 4k. 1513 1514 1515config PCSPKR_PLATFORM 1516 bool "Enable PC-Speaker support" if EXPERT 1517 depends on HAVE_PCSPKR_PLATFORM 1518 select I8253_LOCK 1519 default y 1520 help 1521 This option allows to disable the internal PC-Speaker 1522 support, saving some memory. 1523 1524config BASE_FULL 1525 default y 1526 bool "Enable full-sized data structures for core" if EXPERT 1527 help 1528 Disabling this option reduces the size of miscellaneous core 1529 kernel data structures. This saves memory on small machines, 1530 but may reduce performance. 1531 1532config FUTEX 1533 bool "Enable futex support" if EXPERT 1534 default y 1535 select RT_MUTEXES 1536 help 1537 Disabling this option will cause the kernel to be built without 1538 support for "fast userspace mutexes". The resulting kernel may not 1539 run glibc-based applications correctly. 1540 1541config HAVE_FUTEX_CMPXCHG 1542 bool 1543 depends on FUTEX 1544 help 1545 Architectures should select this if futex_atomic_cmpxchg_inatomic() 1546 is implemented and always working. This removes a couple of runtime 1547 checks. 1548 1549config EPOLL 1550 bool "Enable eventpoll support" if EXPERT 1551 default y 1552 select ANON_INODES 1553 help 1554 Disabling this option will cause the kernel to be built without 1555 support for epoll family of system calls. 1556 1557config SIGNALFD 1558 bool "Enable signalfd() system call" if EXPERT 1559 select ANON_INODES 1560 default y 1561 help 1562 Enable the signalfd() system call that allows to receive signals 1563 on a file descriptor. 1564 1565 If unsure, say Y. 1566 1567config TIMERFD 1568 bool "Enable timerfd() system call" if EXPERT 1569 select ANON_INODES 1570 default y 1571 help 1572 Enable the timerfd() system call that allows to receive timer 1573 events on a file descriptor. 1574 1575 If unsure, say Y. 1576 1577config EVENTFD 1578 bool "Enable eventfd() system call" if EXPERT 1579 select ANON_INODES 1580 default y 1581 help 1582 Enable the eventfd() system call that allows to receive both 1583 kernel notification (ie. KAIO) or userspace notifications. 1584 1585 If unsure, say Y. 1586 1587# syscall, maps, verifier 1588config BPF_SYSCALL 1589 bool "Enable bpf() system call" 1590 select ANON_INODES 1591 select BPF 1592 default n 1593 help 1594 Enable the bpf() system call that allows to manipulate eBPF 1595 programs and maps via file descriptors. 1596 1597config SHMEM 1598 bool "Use full shmem filesystem" if EXPERT 1599 default y 1600 depends on MMU 1601 help 1602 The shmem is an internal filesystem used to manage shared memory. 1603 It is backed by swap and manages resource limits. It is also exported 1604 to userspace as tmpfs if TMPFS is enabled. Disabling this 1605 option replaces shmem and tmpfs with the much simpler ramfs code, 1606 which may be appropriate on small systems without swap. 1607 1608config AIO 1609 bool "Enable AIO support" if EXPERT 1610 default y 1611 help 1612 This option enables POSIX asynchronous I/O which may by used 1613 by some high performance threaded applications. Disabling 1614 this option saves about 7k. 1615 1616config ADVISE_SYSCALLS 1617 bool "Enable madvise/fadvise syscalls" if EXPERT 1618 default y 1619 help 1620 This option enables the madvise and fadvise syscalls, used by 1621 applications to advise the kernel about their future memory or file 1622 usage, improving performance. If building an embedded system where no 1623 applications use these syscalls, you can disable this option to save 1624 space. 1625 1626config USERFAULTFD 1627 bool "Enable userfaultfd() system call" 1628 select ANON_INODES 1629 depends on MMU 1630 help 1631 Enable the userfaultfd() system call that allows to intercept and 1632 handle page faults in userland. 1633 1634config PCI_QUIRKS 1635 default y 1636 bool "Enable PCI quirk workarounds" if EXPERT 1637 depends on PCI 1638 help 1639 This enables workarounds for various PCI chipset 1640 bugs/quirks. Disable this only if your target machine is 1641 unaffected by PCI quirks. 1642 1643config MEMBARRIER 1644 bool "Enable membarrier() system call" if EXPERT 1645 default y 1646 help 1647 Enable the membarrier() system call that allows issuing memory 1648 barriers across all running threads, which can be used to distribute 1649 the cost of user-space memory barriers asymmetrically by transforming 1650 pairs of memory barriers into pairs consisting of membarrier() and a 1651 compiler barrier. 1652 1653 If unsure, say Y. 1654 1655config EMBEDDED 1656 bool "Embedded system" 1657 option allnoconfig_y 1658 select EXPERT 1659 help 1660 This option should be enabled if compiling the kernel for 1661 an embedded system so certain expert options are available 1662 for configuration. 1663 1664config HAVE_PERF_EVENTS 1665 bool 1666 help 1667 See tools/perf/design.txt for details. 1668 1669config PERF_USE_VMALLOC 1670 bool 1671 help 1672 See tools/perf/design.txt for details 1673 1674menu "Kernel Performance Events And Counters" 1675 1676config PERF_EVENTS 1677 bool "Kernel performance events and counters" 1678 default y if PROFILING 1679 depends on HAVE_PERF_EVENTS 1680 select ANON_INODES 1681 select IRQ_WORK 1682 select SRCU 1683 help 1684 Enable kernel support for various performance events provided 1685 by software and hardware. 1686 1687 Software events are supported either built-in or via the 1688 use of generic tracepoints. 1689 1690 Most modern CPUs support performance events via performance 1691 counter registers. These registers count the number of certain 1692 types of hw events: such as instructions executed, cachemisses 1693 suffered, or branches mis-predicted - without slowing down the 1694 kernel or applications. These registers can also trigger interrupts 1695 when a threshold number of events have passed - and can thus be 1696 used to profile the code that runs on that CPU. 1697 1698 The Linux Performance Event subsystem provides an abstraction of 1699 these software and hardware event capabilities, available via a 1700 system call and used by the "perf" utility in tools/perf/. It 1701 provides per task and per CPU counters, and it provides event 1702 capabilities on top of those. 1703 1704 Say Y if unsure. 1705 1706config DEBUG_PERF_USE_VMALLOC 1707 default n 1708 bool "Debug: use vmalloc to back perf mmap() buffers" 1709 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC 1710 select PERF_USE_VMALLOC 1711 help 1712 Use vmalloc memory to back perf mmap() buffers. 1713 1714 Mostly useful for debugging the vmalloc code on platforms 1715 that don't require it. 1716 1717 Say N if unsure. 1718 1719endmenu 1720 1721config VM_EVENT_COUNTERS 1722 default y 1723 bool "Enable VM event counters for /proc/vmstat" if EXPERT 1724 help 1725 VM event counters are needed for event counts to be shown. 1726 This option allows the disabling of the VM event counters 1727 on EXPERT systems. /proc/vmstat will only show page counts 1728 if VM event counters are disabled. 1729 1730config SLUB_DEBUG 1731 default y 1732 bool "Enable SLUB debugging support" if EXPERT 1733 depends on SLUB && SYSFS 1734 help 1735 SLUB has extensive debug support features. Disabling these can 1736 result in significant savings in code size. This also disables 1737 SLUB sysfs support. /sys/slab will not exist and there will be 1738 no support for cache validation etc. 1739 1740config COMPAT_BRK 1741 bool "Disable heap randomization" 1742 default y 1743 help 1744 Randomizing heap placement makes heap exploits harder, but it 1745 also breaks ancient binaries (including anything libc5 based). 1746 This option changes the bootup default to heap randomization 1747 disabled, and can be overridden at runtime by setting 1748 /proc/sys/kernel/randomize_va_space to 2. 1749 1750 On non-ancient distros (post-2000 ones) N is usually a safe choice. 1751 1752choice 1753 prompt "Choose SLAB allocator" 1754 default SLUB 1755 help 1756 This option allows to select a slab allocator. 1757 1758config SLAB 1759 bool "SLAB" 1760 help 1761 The regular slab allocator that is established and known to work 1762 well in all environments. It organizes cache hot objects in 1763 per cpu and per node queues. 1764 1765config SLUB 1766 bool "SLUB (Unqueued Allocator)" 1767 help 1768 SLUB is a slab allocator that minimizes cache line usage 1769 instead of managing queues of cached objects (SLAB approach). 1770 Per cpu caching is realized using slabs of objects instead 1771 of queues of objects. SLUB can use memory efficiently 1772 and has enhanced diagnostics. SLUB is the default choice for 1773 a slab allocator. 1774 1775config SLOB 1776 depends on EXPERT 1777 bool "SLOB (Simple Allocator)" 1778 help 1779 SLOB replaces the stock allocator with a drastically simpler 1780 allocator. SLOB is generally more space efficient but 1781 does not perform as well on large systems. 1782 1783endchoice 1784 1785config SLAB_FREELIST_RANDOM 1786 default n 1787 depends on SLAB 1788 bool "SLAB freelist randomization" 1789 help 1790 Randomizes the freelist order used on creating new SLABs. This 1791 security feature reduces the predictability of the kernel slab 1792 allocator against heap overflows. 1793 1794config SLUB_CPU_PARTIAL 1795 default y 1796 depends on SLUB && SMP 1797 bool "SLUB per cpu partial cache" 1798 help 1799 Per cpu partial caches accellerate objects allocation and freeing 1800 that is local to a processor at the price of more indeterminism 1801 in the latency of the free. On overflow these caches will be cleared 1802 which requires the taking of locks that may cause latency spikes. 1803 Typically one would choose no for a realtime system. 1804 1805config MMAP_ALLOW_UNINITIALIZED 1806 bool "Allow mmapped anonymous memory to be uninitialized" 1807 depends on EXPERT && !MMU 1808 default n 1809 help 1810 Normally, and according to the Linux spec, anonymous memory obtained 1811 from mmap() has it's contents cleared before it is passed to 1812 userspace. Enabling this config option allows you to request that 1813 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus 1814 providing a huge performance boost. If this option is not enabled, 1815 then the flag will be ignored. 1816 1817 This is taken advantage of by uClibc's malloc(), and also by 1818 ELF-FDPIC binfmt's brk and stack allocator. 1819 1820 Because of the obvious security issues, this option should only be 1821 enabled on embedded devices where you control what is run in 1822 userspace. Since that isn't generally a problem on no-MMU systems, 1823 it is normally safe to say Y here. 1824 1825 See Documentation/nommu-mmap.txt for more information. 1826 1827config SYSTEM_DATA_VERIFICATION 1828 def_bool n 1829 select SYSTEM_TRUSTED_KEYRING 1830 select KEYS 1831 select CRYPTO 1832 select CRYPTO_RSA 1833 select ASYMMETRIC_KEY_TYPE 1834 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE 1835 select ASN1 1836 select OID_REGISTRY 1837 select X509_CERTIFICATE_PARSER 1838 select PKCS7_MESSAGE_PARSER 1839 help 1840 Provide PKCS#7 message verification using the contents of the system 1841 trusted keyring to provide public keys. This then can be used for 1842 module verification, kexec image verification and firmware blob 1843 verification. 1844 1845config PROFILING 1846 bool "Profiling support" 1847 help 1848 Say Y here to enable the extended profiling support mechanisms used 1849 by profilers such as OProfile. 1850 1851# 1852# Place an empty function call at each tracepoint site. Can be 1853# dynamically changed for a probe function. 1854# 1855config TRACEPOINTS 1856 bool 1857 1858source "arch/Kconfig" 1859 1860endmenu # General setup 1861 1862config HAVE_GENERIC_DMA_COHERENT 1863 bool 1864 default n 1865 1866config SLABINFO 1867 bool 1868 depends on PROC_FS 1869 depends on SLAB || SLUB_DEBUG 1870 default y 1871 1872config RT_MUTEXES 1873 bool 1874 1875config BASE_SMALL 1876 int 1877 default 0 if BASE_FULL 1878 default 1 if !BASE_FULL 1879 1880menuconfig MODULES 1881 bool "Enable loadable module support" 1882 option modules 1883 help 1884 Kernel modules are small pieces of compiled code which can 1885 be inserted in the running kernel, rather than being 1886 permanently built into the kernel. You use the "modprobe" 1887 tool to add (and sometimes remove) them. If you say Y here, 1888 many parts of the kernel can be built as modules (by 1889 answering M instead of Y where indicated): this is most 1890 useful for infrequently used options which are not required 1891 for booting. For more information, see the man pages for 1892 modprobe, lsmod, modinfo, insmod and rmmod. 1893 1894 If you say Y here, you will need to run "make 1895 modules_install" to put the modules under /lib/modules/ 1896 where modprobe can find them (you may need to be root to do 1897 this). 1898 1899 If unsure, say Y. 1900 1901if MODULES 1902 1903config MODULE_FORCE_LOAD 1904 bool "Forced module loading" 1905 default n 1906 help 1907 Allow loading of modules without version information (ie. modprobe 1908 --force). Forced module loading sets the 'F' (forced) taint flag and 1909 is usually a really bad idea. 1910 1911config MODULE_UNLOAD 1912 bool "Module unloading" 1913 help 1914 Without this option you will not be able to unload any 1915 modules (note that some modules may not be unloadable 1916 anyway), which makes your kernel smaller, faster 1917 and simpler. If unsure, say Y. 1918 1919config MODULE_FORCE_UNLOAD 1920 bool "Forced module unloading" 1921 depends on MODULE_UNLOAD 1922 help 1923 This option allows you to force a module to unload, even if the 1924 kernel believes it is unsafe: the kernel will remove the module 1925 without waiting for anyone to stop using it (using the -f option to 1926 rmmod). This is mainly for kernel developers and desperate users. 1927 If unsure, say N. 1928 1929config MODVERSIONS 1930 bool "Module versioning support" 1931 help 1932 Usually, you have to use modules compiled with your kernel. 1933 Saying Y here makes it sometimes possible to use modules 1934 compiled for different kernels, by adding enough information 1935 to the modules to (hopefully) spot any changes which would 1936 make them incompatible with the kernel you are running. If 1937 unsure, say N. 1938 1939config MODULE_SRCVERSION_ALL 1940 bool "Source checksum for all modules" 1941 help 1942 Modules which contain a MODULE_VERSION get an extra "srcversion" 1943 field inserted into their modinfo section, which contains a 1944 sum of the source files which made it. This helps maintainers 1945 see exactly which source was used to build a module (since 1946 others sometimes change the module source without updating 1947 the version). With this option, such a "srcversion" field 1948 will be created for all modules. If unsure, say N. 1949 1950config MODULE_SIG 1951 bool "Module signature verification" 1952 depends on MODULES 1953 select SYSTEM_DATA_VERIFICATION 1954 help 1955 Check modules for valid signatures upon load: the signature 1956 is simply appended to the module. For more information see 1957 Documentation/module-signing.txt. 1958 1959 Note that this option adds the OpenSSL development packages as a 1960 kernel build dependency so that the signing tool can use its crypto 1961 library. 1962 1963 !!!WARNING!!! If you enable this option, you MUST make sure that the 1964 module DOES NOT get stripped after being signed. This includes the 1965 debuginfo strip done by some packagers (such as rpmbuild) and 1966 inclusion into an initramfs that wants the module size reduced. 1967 1968config MODULE_SIG_FORCE 1969 bool "Require modules to be validly signed" 1970 depends on MODULE_SIG 1971 help 1972 Reject unsigned modules or signed modules for which we don't have a 1973 key. Without this, such modules will simply taint the kernel. 1974 1975config MODULE_SIG_ALL 1976 bool "Automatically sign all modules" 1977 default y 1978 depends on MODULE_SIG 1979 help 1980 Sign all modules during make modules_install. Without this option, 1981 modules must be signed manually, using the scripts/sign-file tool. 1982 1983comment "Do not forget to sign required modules with scripts/sign-file" 1984 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL 1985 1986choice 1987 prompt "Which hash algorithm should modules be signed with?" 1988 depends on MODULE_SIG 1989 help 1990 This determines which sort of hashing algorithm will be used during 1991 signature generation. This algorithm _must_ be built into the kernel 1992 directly so that signature verification can take place. It is not 1993 possible to load a signed module containing the algorithm to check 1994 the signature on that module. 1995 1996config MODULE_SIG_SHA1 1997 bool "Sign modules with SHA-1" 1998 select CRYPTO_SHA1 1999 2000config MODULE_SIG_SHA224 2001 bool "Sign modules with SHA-224" 2002 select CRYPTO_SHA256 2003 2004config MODULE_SIG_SHA256 2005 bool "Sign modules with SHA-256" 2006 select CRYPTO_SHA256 2007 2008config MODULE_SIG_SHA384 2009 bool "Sign modules with SHA-384" 2010 select CRYPTO_SHA512 2011 2012config MODULE_SIG_SHA512 2013 bool "Sign modules with SHA-512" 2014 select CRYPTO_SHA512 2015 2016endchoice 2017 2018config MODULE_SIG_HASH 2019 string 2020 depends on MODULE_SIG 2021 default "sha1" if MODULE_SIG_SHA1 2022 default "sha224" if MODULE_SIG_SHA224 2023 default "sha256" if MODULE_SIG_SHA256 2024 default "sha384" if MODULE_SIG_SHA384 2025 default "sha512" if MODULE_SIG_SHA512 2026 2027config MODULE_COMPRESS 2028 bool "Compress modules on installation" 2029 depends on MODULES 2030 help 2031 2032 Compresses kernel modules when 'make modules_install' is run; gzip or 2033 xz depending on "Compression algorithm" below. 2034 2035 module-init-tools MAY support gzip, and kmod MAY support gzip and xz. 2036 2037 Out-of-tree kernel modules installed using Kbuild will also be 2038 compressed upon installation. 2039 2040 Note: for modules inside an initrd or initramfs, it's more efficient 2041 to compress the whole initrd or initramfs instead. 2042 2043 Note: This is fully compatible with signed modules. 2044 2045 If in doubt, say N. 2046 2047choice 2048 prompt "Compression algorithm" 2049 depends on MODULE_COMPRESS 2050 default MODULE_COMPRESS_GZIP 2051 help 2052 This determines which sort of compression will be used during 2053 'make modules_install'. 2054 2055 GZIP (default) and XZ are supported. 2056 2057config MODULE_COMPRESS_GZIP 2058 bool "GZIP" 2059 2060config MODULE_COMPRESS_XZ 2061 bool "XZ" 2062 2063endchoice 2064 2065config TRIM_UNUSED_KSYMS 2066 bool "Trim unused exported kernel symbols" 2067 depends on MODULES && !UNUSED_SYMBOLS 2068 help 2069 The kernel and some modules make many symbols available for 2070 other modules to use via EXPORT_SYMBOL() and variants. Depending 2071 on the set of modules being selected in your kernel configuration, 2072 many of those exported symbols might never be used. 2073 2074 This option allows for unused exported symbols to be dropped from 2075 the build. In turn, this provides the compiler more opportunities 2076 (especially when using LTO) for optimizing the code and reducing 2077 binary size. This might have some security advantages as well. 2078 2079 If unsure say N. 2080 2081endif # MODULES 2082 2083config MODULES_TREE_LOOKUP 2084 def_bool y 2085 depends on PERF_EVENTS || TRACING 2086 2087config INIT_ALL_POSSIBLE 2088 bool 2089 help 2090 Back when each arch used to define their own cpu_online_mask and 2091 cpu_possible_mask, some of them chose to initialize cpu_possible_mask 2092 with all 1s, and others with all 0s. When they were centralised, 2093 it was better to provide this option than to break all the archs 2094 and have several arch maintainers pursuing me down dark alleys. 2095 2096source "block/Kconfig" 2097 2098config PREEMPT_NOTIFIERS 2099 bool 2100 2101config PADATA 2102 depends on SMP 2103 bool 2104 2105# Can be selected by architectures with broken toolchains 2106# that get confused by correct const<->read_only section 2107# mappings 2108config BROKEN_RODATA 2109 bool 2110 2111config ASN1 2112 tristate 2113 help 2114 Build a simple ASN.1 grammar compiler that produces a bytecode output 2115 that can be interpreted by the ASN.1 stream decoder and used to 2116 inform it as to what tags are to be expected in a stream and what 2117 functions to call on what tags. 2118 2119source "kernel/Kconfig.locks" 2120