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" 276 select EXPORTFS 277 help 278 If you say Y here, a user level program will be able to map 279 file names to handle and then later use the handle for 280 different file system operations. This is useful in implementing 281 userspace file servers, which now track files using handles instead 282 of names. The handle would remain the same even if file names 283 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2) 284 syscalls. 285 286config USELIB 287 bool "uselib syscall" 288 default y 289 help 290 This option enables the uselib syscall, a system call used in the 291 dynamic linker from libc5 and earlier. glibc does not use this 292 system call. If you intend to run programs built on libc5 or 293 earlier, you may need to enable this syscall. Current systems 294 running glibc can safely disable this. 295 296config AUDIT 297 bool "Auditing support" 298 depends on NET 299 help 300 Enable auditing infrastructure that can be used with another 301 kernel subsystem, such as SELinux (which requires this for 302 logging of avc messages output). Does not do system-call 303 auditing without CONFIG_AUDITSYSCALL. 304 305config HAVE_ARCH_AUDITSYSCALL 306 bool 307 308config AUDITSYSCALL 309 bool "Enable system-call auditing support" 310 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL 311 default y if SECURITY_SELINUX 312 help 313 Enable low-overhead system-call auditing infrastructure that 314 can be used independently or with another kernel subsystem, 315 such as SELinux. 316 317config AUDIT_WATCH 318 def_bool y 319 depends on AUDITSYSCALL 320 select FSNOTIFY 321 322config AUDIT_TREE 323 def_bool y 324 depends on AUDITSYSCALL 325 select FSNOTIFY 326 327source "kernel/irq/Kconfig" 328source "kernel/time/Kconfig" 329 330menu "CPU/Task time and stats accounting" 331 332config VIRT_CPU_ACCOUNTING 333 bool 334 335choice 336 prompt "Cputime accounting" 337 default TICK_CPU_ACCOUNTING if !PPC64 338 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64 339 340# Kind of a stub config for the pure tick based cputime accounting 341config TICK_CPU_ACCOUNTING 342 bool "Simple tick based cputime accounting" 343 depends on !S390 && !NO_HZ_FULL 344 help 345 This is the basic tick based cputime accounting that maintains 346 statistics about user, system and idle time spent on per jiffies 347 granularity. 348 349 If unsure, say Y. 350 351config VIRT_CPU_ACCOUNTING_NATIVE 352 bool "Deterministic task and CPU time accounting" 353 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL 354 select VIRT_CPU_ACCOUNTING 355 help 356 Select this option to enable more accurate task and CPU time 357 accounting. This is done by reading a CPU counter on each 358 kernel entry and exit and on transitions within the kernel 359 between system, softirq and hardirq state, so there is a 360 small performance impact. In the case of s390 or IBM POWER > 5, 361 this also enables accounting of stolen time on logically-partitioned 362 systems. 363 364config VIRT_CPU_ACCOUNTING_GEN 365 bool "Full dynticks CPU time accounting" 366 depends on HAVE_CONTEXT_TRACKING 367 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 368 select VIRT_CPU_ACCOUNTING 369 select CONTEXT_TRACKING 370 help 371 Select this option to enable task and CPU time accounting on full 372 dynticks systems. This accounting is implemented by watching every 373 kernel-user boundaries using the context tracking subsystem. 374 The accounting is thus performed at the expense of some significant 375 overhead. 376 377 For now this is only useful if you are working on the full 378 dynticks subsystem development. 379 380 If unsure, say N. 381 382config IRQ_TIME_ACCOUNTING 383 bool "Fine granularity task level IRQ time accounting" 384 depends on HAVE_IRQ_TIME_ACCOUNTING && !NO_HZ_FULL 385 help 386 Select this option to enable fine granularity task irq time 387 accounting. This is done by reading a timestamp on each 388 transitions between softirq and hardirq state, so there can be a 389 small performance impact. 390 391 If in doubt, say N here. 392 393endchoice 394 395config BSD_PROCESS_ACCT 396 bool "BSD Process Accounting" 397 depends on MULTIUSER 398 help 399 If you say Y here, a user level program will be able to instruct the 400 kernel (via a special system call) to write process accounting 401 information to a file: whenever a process exits, information about 402 that process will be appended to the file by the kernel. The 403 information includes things such as creation time, owning user, 404 command name, memory usage, controlling terminal etc. (the complete 405 list is in the struct acct in <file:include/linux/acct.h>). It is 406 up to the user level program to do useful things with this 407 information. This is generally a good idea, so say Y. 408 409config BSD_PROCESS_ACCT_V3 410 bool "BSD Process Accounting version 3 file format" 411 depends on BSD_PROCESS_ACCT 412 default n 413 help 414 If you say Y here, the process accounting information is written 415 in a new file format that also logs the process IDs of each 416 process and it's parent. Note that this file format is incompatible 417 with previous v0/v1/v2 file formats, so you will need updated tools 418 for processing it. A preliminary version of these tools is available 419 at <http://www.gnu.org/software/acct/>. 420 421config TASKSTATS 422 bool "Export task/process statistics through netlink" 423 depends on NET 424 depends on MULTIUSER 425 default n 426 help 427 Export selected statistics for tasks/processes through the 428 generic netlink interface. Unlike BSD process accounting, the 429 statistics are available during the lifetime of tasks/processes as 430 responses to commands. Like BSD accounting, they are sent to user 431 space on task exit. 432 433 Say N if unsure. 434 435config TASK_DELAY_ACCT 436 bool "Enable per-task delay accounting" 437 depends on TASKSTATS 438 help 439 Collect information on time spent by a task waiting for system 440 resources like cpu, synchronous block I/O completion and swapping 441 in pages. Such statistics can help in setting a task's priorities 442 relative to other tasks for cpu, io, rss limits etc. 443 444 Say N if unsure. 445 446config TASK_XACCT 447 bool "Enable extended accounting over taskstats" 448 depends on TASKSTATS 449 help 450 Collect extended task accounting data and send the data 451 to userland for processing over the taskstats interface. 452 453 Say N if unsure. 454 455config TASK_IO_ACCOUNTING 456 bool "Enable per-task storage I/O accounting" 457 depends on TASK_XACCT 458 help 459 Collect information on the number of bytes of storage I/O which this 460 task has caused. 461 462 Say N if unsure. 463 464endmenu # "CPU/Task time and stats accounting" 465 466menu "RCU Subsystem" 467 468config TREE_RCU 469 bool 470 default y if !PREEMPT && SMP 471 help 472 This option selects the RCU implementation that is 473 designed for very large SMP system with hundreds or 474 thousands of CPUs. It also scales down nicely to 475 smaller systems. 476 477config PREEMPT_RCU 478 bool 479 default y if PREEMPT 480 help 481 This option selects the RCU implementation that is 482 designed for very large SMP systems with hundreds or 483 thousands of CPUs, but for which real-time response 484 is also required. It also scales down nicely to 485 smaller systems. 486 487 Select this option if you are unsure. 488 489config TINY_RCU 490 bool 491 default y if !PREEMPT && !SMP 492 help 493 This option selects the RCU implementation that is 494 designed for UP systems from which real-time response 495 is not required. This option greatly reduces the 496 memory footprint of RCU. 497 498config RCU_EXPERT 499 bool "Make expert-level adjustments to RCU configuration" 500 default n 501 help 502 This option needs to be enabled if you wish to make 503 expert-level adjustments to RCU configuration. By default, 504 no such adjustments can be made, which has the often-beneficial 505 side-effect of preventing "make oldconfig" from asking you all 506 sorts of detailed questions about how you would like numerous 507 obscure RCU options to be set up. 508 509 Say Y if you need to make expert-level adjustments to RCU. 510 511 Say N if you are unsure. 512 513config SRCU 514 bool 515 help 516 This option selects the sleepable version of RCU. This version 517 permits arbitrary sleeping or blocking within RCU read-side critical 518 sections. 519 520config TASKS_RCU 521 bool 522 default n 523 select SRCU 524 help 525 This option enables a task-based RCU implementation that uses 526 only voluntary context switch (not preemption!), idle, and 527 user-mode execution as quiescent states. 528 529config RCU_STALL_COMMON 530 def_bool ( TREE_RCU || PREEMPT_RCU || RCU_TRACE ) 531 help 532 This option enables RCU CPU stall code that is common between 533 the TINY and TREE variants of RCU. The purpose is to allow 534 the tiny variants to disable RCU CPU stall warnings, while 535 making these warnings mandatory for the tree variants. 536 537config CONTEXT_TRACKING 538 bool 539 540config RCU_USER_QS 541 bool 542 help 543 This option sets hooks on kernel / userspace boundaries and 544 puts RCU in extended quiescent state when the CPU runs in 545 userspace. It means that when a CPU runs in userspace, it is 546 excluded from the global RCU state machine and thus doesn't 547 try to keep the timer tick on for RCU. 548 549config CONTEXT_TRACKING_FORCE 550 bool "Force context tracking" 551 depends on CONTEXT_TRACKING 552 default y if !NO_HZ_FULL 553 help 554 The major pre-requirement for full dynticks to work is to 555 support the context tracking subsystem. But there are also 556 other dependencies to provide in order to make the full 557 dynticks working. 558 559 This option stands for testing when an arch implements the 560 context tracking backend but doesn't yet fullfill all the 561 requirements to make the full dynticks feature working. 562 Without the full dynticks, there is no way to test the support 563 for context tracking and the subsystems that rely on it: RCU 564 userspace extended quiescent state and tickless cputime 565 accounting. This option copes with the absence of the full 566 dynticks subsystem by forcing the context tracking on all 567 CPUs in the system. 568 569 Say Y only if you're working on the development of an 570 architecture backend for the context tracking. 571 572 Say N otherwise, this option brings an overhead that you 573 don't want in production. 574 575 576config RCU_FANOUT 577 int "Tree-based hierarchical RCU fanout value" 578 range 2 64 if 64BIT 579 range 2 32 if !64BIT 580 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT 581 default 64 if 64BIT 582 default 32 if !64BIT 583 help 584 This option controls the fanout of hierarchical implementations 585 of RCU, allowing RCU to work efficiently on machines with 586 large numbers of CPUs. This value must be at least the fourth 587 root of NR_CPUS, which allows NR_CPUS to be insanely large. 588 The default value of RCU_FANOUT should be used for production 589 systems, but if you are stress-testing the RCU implementation 590 itself, small RCU_FANOUT values allow you to test large-system 591 code paths on small(er) systems. 592 593 Select a specific number if testing RCU itself. 594 Take the default if unsure. 595 596config RCU_FANOUT_LEAF 597 int "Tree-based hierarchical RCU leaf-level fanout value" 598 range 2 64 if 64BIT 599 range 2 32 if !64BIT 600 depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT 601 default 16 602 help 603 This option controls the leaf-level fanout of hierarchical 604 implementations of RCU, and allows trading off cache misses 605 against lock contention. Systems that synchronize their 606 scheduling-clock interrupts for energy-efficiency reasons will 607 want the default because the smaller leaf-level fanout keeps 608 lock contention levels acceptably low. Very large systems 609 (hundreds or thousands of CPUs) will instead want to set this 610 value to the maximum value possible in order to reduce the 611 number of cache misses incurred during RCU's grace-period 612 initialization. These systems tend to run CPU-bound, and thus 613 are not helped by synchronized interrupts, and thus tend to 614 skew them, which reduces lock contention enough that large 615 leaf-level fanouts work well. 616 617 Select a specific number if testing RCU itself. 618 619 Select the maximum permissible value for large systems. 620 621 Take the default if unsure. 622 623config RCU_FAST_NO_HZ 624 bool "Accelerate last non-dyntick-idle CPU's grace periods" 625 depends on NO_HZ_COMMON && SMP && RCU_EXPERT 626 default n 627 help 628 This option permits CPUs to enter dynticks-idle state even if 629 they have RCU callbacks queued, and prevents RCU from waking 630 these CPUs up more than roughly once every four jiffies (by 631 default, you can adjust this using the rcutree.rcu_idle_gp_delay 632 parameter), thus improving energy efficiency. On the other 633 hand, this option increases the duration of RCU grace periods, 634 for example, slowing down synchronize_rcu(). 635 636 Say Y if energy efficiency is critically important, and you 637 don't care about increased grace-period durations. 638 639 Say N if you are unsure. 640 641config TREE_RCU_TRACE 642 def_bool RCU_TRACE && ( TREE_RCU || PREEMPT_RCU ) 643 select DEBUG_FS 644 help 645 This option provides tracing for the TREE_RCU and 646 PREEMPT_RCU implementations, permitting Makefile to 647 trivially select kernel/rcutree_trace.c. 648 649config RCU_BOOST 650 bool "Enable RCU priority boosting" 651 depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT 652 default n 653 help 654 This option boosts the priority of preempted RCU readers that 655 block the current preemptible RCU grace period for too long. 656 This option also prevents heavy loads from blocking RCU 657 callback invocation for all flavors of RCU. 658 659 Say Y here if you are working with real-time apps or heavy loads 660 Say N here if you are unsure. 661 662config RCU_KTHREAD_PRIO 663 int "Real-time priority to use for RCU worker threads" 664 range 1 99 if RCU_BOOST 665 range 0 99 if !RCU_BOOST 666 default 1 if RCU_BOOST 667 default 0 if !RCU_BOOST 668 depends on RCU_EXPERT 669 help 670 This option specifies the SCHED_FIFO priority value that will be 671 assigned to the rcuc/n and rcub/n threads and is also the value 672 used for RCU_BOOST (if enabled). If you are working with a 673 real-time application that has one or more CPU-bound threads 674 running at a real-time priority level, you should set 675 RCU_KTHREAD_PRIO to a priority higher than the highest-priority 676 real-time CPU-bound application thread. The default RCU_KTHREAD_PRIO 677 value of 1 is appropriate in the common case, which is real-time 678 applications that do not have any CPU-bound threads. 679 680 Some real-time applications might not have a single real-time 681 thread that saturates a given CPU, but instead might have 682 multiple real-time threads that, taken together, fully utilize 683 that CPU. In this case, you should set RCU_KTHREAD_PRIO to 684 a priority higher than the lowest-priority thread that is 685 conspiring to prevent the CPU from running any non-real-time 686 tasks. For example, if one thread at priority 10 and another 687 thread at priority 5 are between themselves fully consuming 688 the CPU time on a given CPU, then RCU_KTHREAD_PRIO should be 689 set to priority 6 or higher. 690 691 Specify the real-time priority, or take the default if unsure. 692 693config RCU_BOOST_DELAY 694 int "Milliseconds to delay boosting after RCU grace-period start" 695 range 0 3000 696 depends on RCU_BOOST 697 default 500 698 help 699 This option specifies the time to wait after the beginning of 700 a given grace period before priority-boosting preempted RCU 701 readers blocking that grace period. Note that any RCU reader 702 blocking an expedited RCU grace period is boosted immediately. 703 704 Accept the default if unsure. 705 706config RCU_NOCB_CPU 707 bool "Offload RCU callback processing from boot-selected CPUs" 708 depends on TREE_RCU || PREEMPT_RCU 709 default n 710 help 711 Use this option to reduce OS jitter for aggressive HPC or 712 real-time workloads. It can also be used to offload RCU 713 callback invocation to energy-efficient CPUs in battery-powered 714 asymmetric multiprocessors. 715 716 This option offloads callback invocation from the set of 717 CPUs specified at boot time by the rcu_nocbs parameter. 718 For each such CPU, a kthread ("rcuox/N") will be created to 719 invoke callbacks, where the "N" is the CPU being offloaded, 720 and where the "x" is "b" for RCU-bh, "p" for RCU-preempt, and 721 "s" for RCU-sched. Nothing prevents this kthread from running 722 on the specified CPUs, but (1) the kthreads may be preempted 723 between each callback, and (2) affinity or cgroups can be used 724 to force the kthreads to run on whatever set of CPUs is desired. 725 726 Say Y here if you want to help to debug reduced OS jitter. 727 Say N here if you are unsure. 728 729choice 730 prompt "Build-forced no-CBs CPUs" 731 default RCU_NOCB_CPU_NONE 732 depends on RCU_NOCB_CPU 733 help 734 This option allows no-CBs CPUs (whose RCU callbacks are invoked 735 from kthreads rather than from softirq context) to be specified 736 at build time. Additional no-CBs CPUs may be specified by 737 the rcu_nocbs= boot parameter. 738 739config RCU_NOCB_CPU_NONE 740 bool "No build_forced no-CBs CPUs" 741 help 742 This option does not force any of the CPUs to be no-CBs CPUs. 743 Only CPUs designated by the rcu_nocbs= boot parameter will be 744 no-CBs CPUs, whose RCU callbacks will be invoked by per-CPU 745 kthreads whose names begin with "rcuo". All other CPUs will 746 invoke their own RCU callbacks in softirq context. 747 748 Select this option if you want to choose no-CBs CPUs at 749 boot time, for example, to allow testing of different no-CBs 750 configurations without having to rebuild the kernel each time. 751 752config RCU_NOCB_CPU_ZERO 753 bool "CPU 0 is a build_forced no-CBs CPU" 754 help 755 This option forces CPU 0 to be a no-CBs CPU, so that its RCU 756 callbacks are invoked by a per-CPU kthread whose name begins 757 with "rcuo". Additional CPUs may be designated as no-CBs 758 CPUs using the rcu_nocbs= boot parameter will be no-CBs CPUs. 759 All other CPUs will invoke their own RCU callbacks in softirq 760 context. 761 762 Select this if CPU 0 needs to be a no-CBs CPU for real-time 763 or energy-efficiency reasons, but the real reason it exists 764 is to ensure that randconfig testing covers mixed systems. 765 766config RCU_NOCB_CPU_ALL 767 bool "All CPUs are build_forced no-CBs CPUs" 768 help 769 This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs= 770 boot parameter will be ignored. All CPUs' RCU callbacks will 771 be executed in the context of per-CPU rcuo kthreads created for 772 this purpose. Assuming that the kthreads whose names start with 773 "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter 774 on the remaining CPUs, but might decrease memory locality during 775 RCU-callback invocation, thus potentially degrading throughput. 776 777 Select this if all CPUs need to be no-CBs CPUs for real-time 778 or energy-efficiency reasons. 779 780endchoice 781 782config RCU_EXPEDITE_BOOT 783 bool 784 default n 785 help 786 This option enables expedited grace periods at boot time, 787 as if rcu_expedite_gp() had been invoked early in boot. 788 The corresponding rcu_unexpedite_gp() is invoked from 789 rcu_end_inkernel_boot(), which is intended to be invoked 790 at the end of the kernel-only boot sequence, just before 791 init is exec'ed. 792 793 Accept the default if unsure. 794 795endmenu # "RCU Subsystem" 796 797config BUILD_BIN2C 798 bool 799 default n 800 801config IKCONFIG 802 tristate "Kernel .config support" 803 select BUILD_BIN2C 804 ---help--- 805 This option enables the complete Linux kernel ".config" file 806 contents to be saved in the kernel. It provides documentation 807 of which kernel options are used in a running kernel or in an 808 on-disk kernel. This information can be extracted from the kernel 809 image file with the script scripts/extract-ikconfig and used as 810 input to rebuild the current kernel or to build another kernel. 811 It can also be extracted from a running kernel by reading 812 /proc/config.gz if enabled (below). 813 814config IKCONFIG_PROC 815 bool "Enable access to .config through /proc/config.gz" 816 depends on IKCONFIG && PROC_FS 817 ---help--- 818 This option enables access to the kernel configuration file 819 through /proc/config.gz. 820 821config LOG_BUF_SHIFT 822 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)" 823 range 12 21 824 default 17 825 depends on PRINTK 826 help 827 Select the minimal kernel log buffer size as a power of 2. 828 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config 829 parameter, see below. Any higher size also might be forced 830 by "log_buf_len" boot parameter. 831 832 Examples: 833 17 => 128 KB 834 16 => 64 KB 835 15 => 32 KB 836 14 => 16 KB 837 13 => 8 KB 838 12 => 4 KB 839 840config LOG_CPU_MAX_BUF_SHIFT 841 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)" 842 depends on SMP 843 range 0 21 844 default 12 if !BASE_SMALL 845 default 0 if BASE_SMALL 846 depends on PRINTK 847 help 848 This option allows to increase the default ring buffer size 849 according to the number of CPUs. The value defines the contribution 850 of each CPU as a power of 2. The used space is typically only few 851 lines however it might be much more when problems are reported, 852 e.g. backtraces. 853 854 The increased size means that a new buffer has to be allocated and 855 the original static one is unused. It makes sense only on systems 856 with more CPUs. Therefore this value is used only when the sum of 857 contributions is greater than the half of the default kernel ring 858 buffer as defined by LOG_BUF_SHIFT. The default values are set 859 so that more than 64 CPUs are needed to trigger the allocation. 860 861 Also this option is ignored when "log_buf_len" kernel parameter is 862 used as it forces an exact (power of two) size of the ring buffer. 863 864 The number of possible CPUs is used for this computation ignoring 865 hotplugging making the compuation optimal for the the worst case 866 scenerio while allowing a simple algorithm to be used from bootup. 867 868 Examples shift values and their meaning: 869 17 => 128 KB for each CPU 870 16 => 64 KB for each CPU 871 15 => 32 KB for each CPU 872 14 => 16 KB for each CPU 873 13 => 8 KB for each CPU 874 12 => 4 KB for each CPU 875 876# 877# Architectures with an unreliable sched_clock() should select this: 878# 879config HAVE_UNSTABLE_SCHED_CLOCK 880 bool 881 882config GENERIC_SCHED_CLOCK 883 bool 884 885# 886# For architectures that want to enable the support for NUMA-affine scheduler 887# balancing logic: 888# 889config ARCH_SUPPORTS_NUMA_BALANCING 890 bool 891 892# 893# For architectures that know their GCC __int128 support is sound 894# 895config ARCH_SUPPORTS_INT128 896 bool 897 898# For architectures that (ab)use NUMA to represent different memory regions 899# all cpu-local but of different latencies, such as SuperH. 900# 901config ARCH_WANT_NUMA_VARIABLE_LOCALITY 902 bool 903 904config NUMA_BALANCING 905 bool "Memory placement aware NUMA scheduler" 906 depends on ARCH_SUPPORTS_NUMA_BALANCING 907 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY 908 depends on SMP && NUMA && MIGRATION 909 help 910 This option adds support for automatic NUMA aware memory/task placement. 911 The mechanism is quite primitive and is based on migrating memory when 912 it has references to the node the task is running on. 913 914 This system will be inactive on UMA systems. 915 916config NUMA_BALANCING_DEFAULT_ENABLED 917 bool "Automatically enable NUMA aware memory/task placement" 918 default y 919 depends on NUMA_BALANCING 920 help 921 If set, automatic NUMA balancing will be enabled if running on a NUMA 922 machine. 923 924menuconfig CGROUPS 925 bool "Control Group support" 926 select KERNFS 927 select PERCPU_RWSEM 928 help 929 This option adds support for grouping sets of processes together, for 930 use with process control subsystems such as Cpusets, CFS, memory 931 controls or device isolation. 932 See 933 - Documentation/scheduler/sched-design-CFS.txt (CFS) 934 - Documentation/cgroups/ (features for grouping, isolation 935 and resource control) 936 937 Say N if unsure. 938 939if CGROUPS 940 941config CGROUP_DEBUG 942 bool "Example debug cgroup subsystem" 943 default n 944 help 945 This option enables a simple cgroup subsystem that 946 exports useful debugging information about the cgroups 947 framework. 948 949 Say N if unsure. 950 951config CGROUP_FREEZER 952 bool "Freezer cgroup subsystem" 953 help 954 Provides a way to freeze and unfreeze all tasks in a 955 cgroup. 956 957config CGROUP_DEVICE 958 bool "Device controller for cgroups" 959 help 960 Provides a cgroup implementing whitelists for devices which 961 a process in the cgroup can mknod or open. 962 963config CPUSETS 964 bool "Cpuset support" 965 help 966 This option will let you create and manage CPUSETs which 967 allow dynamically partitioning a system into sets of CPUs and 968 Memory Nodes and assigning tasks to run only within those sets. 969 This is primarily useful on large SMP or NUMA systems. 970 971 Say N if unsure. 972 973config PROC_PID_CPUSET 974 bool "Include legacy /proc/<pid>/cpuset file" 975 depends on CPUSETS 976 default y 977 978config CGROUP_CPUACCT 979 bool "Simple CPU accounting cgroup subsystem" 980 help 981 Provides a simple Resource Controller for monitoring the 982 total CPU consumed by the tasks in a cgroup. 983 984config PAGE_COUNTER 985 bool 986 987config MEMCG 988 bool "Memory Resource Controller for Control Groups" 989 select PAGE_COUNTER 990 select EVENTFD 991 help 992 Provides a memory resource controller that manages both anonymous 993 memory and page cache. (See Documentation/cgroups/memory.txt) 994 995config MEMCG_SWAP 996 bool "Memory Resource Controller Swap Extension" 997 depends on MEMCG && SWAP 998 help 999 Add swap management feature to memory resource controller. When you 1000 enable this, you can limit mem+swap usage per cgroup. In other words, 1001 when you disable this, memory resource controller has no cares to 1002 usage of swap...a process can exhaust all of the swap. This extension 1003 is useful when you want to avoid exhaustion swap but this itself 1004 adds more overheads and consumes memory for remembering information. 1005 Especially if you use 32bit system or small memory system, please 1006 be careful about enabling this. When memory resource controller 1007 is disabled by boot option, this will be automatically disabled and 1008 there will be no overhead from this. Even when you set this config=y, 1009 if boot option "swapaccount=0" is set, swap will not be accounted. 1010 Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page 1011 size is 4096bytes, 512k per 1Gbytes of swap. 1012config MEMCG_SWAP_ENABLED 1013 bool "Memory Resource Controller Swap Extension enabled by default" 1014 depends on MEMCG_SWAP 1015 default y 1016 help 1017 Memory Resource Controller Swap Extension comes with its price in 1018 a bigger memory consumption. General purpose distribution kernels 1019 which want to enable the feature but keep it disabled by default 1020 and let the user enable it by swapaccount=1 boot command line 1021 parameter should have this option unselected. 1022 For those who want to have the feature enabled by default should 1023 select this option (if, for some reason, they need to disable it 1024 then swapaccount=0 does the trick). 1025config MEMCG_KMEM 1026 bool "Memory Resource Controller Kernel Memory accounting" 1027 depends on MEMCG 1028 depends on SLUB || SLAB 1029 help 1030 The Kernel Memory extension for Memory Resource Controller can limit 1031 the amount of memory used by kernel objects in the system. Those are 1032 fundamentally different from the entities handled by the standard 1033 Memory Controller, which are page-based, and can be swapped. Users of 1034 the kmem extension can use it to guarantee that no group of processes 1035 will ever exhaust kernel resources alone. 1036 1037config CGROUP_HUGETLB 1038 bool "HugeTLB Resource Controller for Control Groups" 1039 depends on HUGETLB_PAGE 1040 select PAGE_COUNTER 1041 default n 1042 help 1043 Provides a cgroup Resource Controller for HugeTLB pages. 1044 When you enable this, you can put a per cgroup limit on HugeTLB usage. 1045 The limit is enforced during page fault. Since HugeTLB doesn't 1046 support page reclaim, enforcing the limit at page fault time implies 1047 that, the application will get SIGBUS signal if it tries to access 1048 HugeTLB pages beyond its limit. This requires the application to know 1049 beforehand how much HugeTLB pages it would require for its use. The 1050 control group is tracked in the third page lru pointer. This means 1051 that we cannot use the controller with huge page less than 3 pages. 1052 1053config CGROUP_PERF 1054 bool "Enable perf_event per-cpu per-container group (cgroup) monitoring" 1055 depends on PERF_EVENTS && CGROUPS 1056 help 1057 This option extends the per-cpu mode to restrict monitoring to 1058 threads which belong to the cgroup specified and run on the 1059 designated cpu. 1060 1061 Say N if unsure. 1062 1063menuconfig CGROUP_SCHED 1064 bool "Group CPU scheduler" 1065 default n 1066 help 1067 This feature lets CPU scheduler recognize task groups and control CPU 1068 bandwidth allocation to such task groups. It uses cgroups to group 1069 tasks. 1070 1071if CGROUP_SCHED 1072config FAIR_GROUP_SCHED 1073 bool "Group scheduling for SCHED_OTHER" 1074 depends on CGROUP_SCHED 1075 default CGROUP_SCHED 1076 1077config CFS_BANDWIDTH 1078 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED" 1079 depends on FAIR_GROUP_SCHED 1080 default n 1081 help 1082 This option allows users to define CPU bandwidth rates (limits) for 1083 tasks running within the fair group scheduler. Groups with no limit 1084 set are considered to be unconstrained and will run with no 1085 restriction. 1086 See tip/Documentation/scheduler/sched-bwc.txt for more information. 1087 1088config RT_GROUP_SCHED 1089 bool "Group scheduling for SCHED_RR/FIFO" 1090 depends on CGROUP_SCHED 1091 default n 1092 help 1093 This feature lets you explicitly allocate real CPU bandwidth 1094 to task groups. If enabled, it will also make it impossible to 1095 schedule realtime tasks for non-root users until you allocate 1096 realtime bandwidth for them. 1097 See Documentation/scheduler/sched-rt-group.txt for more information. 1098 1099endif #CGROUP_SCHED 1100 1101config BLK_CGROUP 1102 bool "Block IO controller" 1103 depends on BLOCK 1104 default n 1105 ---help--- 1106 Generic block IO controller cgroup interface. This is the common 1107 cgroup interface which should be used by various IO controlling 1108 policies. 1109 1110 Currently, CFQ IO scheduler uses it to recognize task groups and 1111 control disk bandwidth allocation (proportional time slice allocation) 1112 to such task groups. It is also used by bio throttling logic in 1113 block layer to implement upper limit in IO rates on a device. 1114 1115 This option only enables generic Block IO controller infrastructure. 1116 One needs to also enable actual IO controlling logic/policy. For 1117 enabling proportional weight division of disk bandwidth in CFQ, set 1118 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set 1119 CONFIG_BLK_DEV_THROTTLING=y. 1120 1121 See Documentation/cgroups/blkio-controller.txt for more information. 1122 1123config DEBUG_BLK_CGROUP 1124 bool "Enable Block IO controller debugging" 1125 depends on BLK_CGROUP 1126 default n 1127 ---help--- 1128 Enable some debugging help. Currently it exports additional stat 1129 files in a cgroup which can be useful for debugging. 1130 1131config CGROUP_WRITEBACK 1132 bool 1133 depends on MEMCG && BLK_CGROUP 1134 default y 1135 1136endif # CGROUPS 1137 1138config CHECKPOINT_RESTORE 1139 bool "Checkpoint/restore support" if EXPERT 1140 select PROC_CHILDREN 1141 default n 1142 help 1143 Enables additional kernel features in a sake of checkpoint/restore. 1144 In particular it adds auxiliary prctl codes to setup process text, 1145 data and heap segment sizes, and a few additional /proc filesystem 1146 entries. 1147 1148 If unsure, say N here. 1149 1150menuconfig NAMESPACES 1151 bool "Namespaces support" if EXPERT 1152 depends on MULTIUSER 1153 default !EXPERT 1154 help 1155 Provides the way to make tasks work with different objects using 1156 the same id. For example same IPC id may refer to different objects 1157 or same user id or pid may refer to different tasks when used in 1158 different namespaces. 1159 1160if NAMESPACES 1161 1162config UTS_NS 1163 bool "UTS namespace" 1164 default y 1165 help 1166 In this namespace tasks see different info provided with the 1167 uname() system call 1168 1169config IPC_NS 1170 bool "IPC namespace" 1171 depends on (SYSVIPC || POSIX_MQUEUE) 1172 default y 1173 help 1174 In this namespace tasks work with IPC ids which correspond to 1175 different IPC objects in different namespaces. 1176 1177config USER_NS 1178 bool "User namespace" 1179 default n 1180 help 1181 This allows containers, i.e. vservers, to use user namespaces 1182 to provide different user info for different servers. 1183 1184 When user namespaces are enabled in the kernel it is 1185 recommended that the MEMCG and MEMCG_KMEM options also be 1186 enabled and that user-space use the memory control groups to 1187 limit the amount of memory a memory unprivileged users can 1188 use. 1189 1190 If unsure, say N. 1191 1192config PID_NS 1193 bool "PID Namespaces" 1194 default y 1195 help 1196 Support process id namespaces. This allows having multiple 1197 processes with the same pid as long as they are in different 1198 pid namespaces. This is a building block of containers. 1199 1200config NET_NS 1201 bool "Network namespace" 1202 depends on NET 1203 default y 1204 help 1205 Allow user space to create what appear to be multiple instances 1206 of the network stack. 1207 1208endif # NAMESPACES 1209 1210config SCHED_AUTOGROUP 1211 bool "Automatic process group scheduling" 1212 select CGROUPS 1213 select CGROUP_SCHED 1214 select FAIR_GROUP_SCHED 1215 help 1216 This option optimizes the scheduler for common desktop workloads by 1217 automatically creating and populating task groups. This separation 1218 of workloads isolates aggressive CPU burners (like build jobs) from 1219 desktop applications. Task group autogeneration is currently based 1220 upon task session. 1221 1222config SYSFS_DEPRECATED 1223 bool "Enable deprecated sysfs features to support old userspace tools" 1224 depends on SYSFS 1225 default n 1226 help 1227 This option adds code that switches the layout of the "block" class 1228 devices, to not show up in /sys/class/block/, but only in 1229 /sys/block/. 1230 1231 This switch is only active when the sysfs.deprecated=1 boot option is 1232 passed or the SYSFS_DEPRECATED_V2 option is set. 1233 1234 This option allows new kernels to run on old distributions and tools, 1235 which might get confused by /sys/class/block/. Since 2007/2008 all 1236 major distributions and tools handle this just fine. 1237 1238 Recent distributions and userspace tools after 2009/2010 depend on 1239 the existence of /sys/class/block/, and will not work with this 1240 option enabled. 1241 1242 Only if you are using a new kernel on an old distribution, you might 1243 need to say Y here. 1244 1245config SYSFS_DEPRECATED_V2 1246 bool "Enable deprecated sysfs features by default" 1247 default n 1248 depends on SYSFS 1249 depends on SYSFS_DEPRECATED 1250 help 1251 Enable deprecated sysfs by default. 1252 1253 See the CONFIG_SYSFS_DEPRECATED option for more details about this 1254 option. 1255 1256 Only if you are using a new kernel on an old distribution, you might 1257 need to say Y here. Even then, odds are you would not need it 1258 enabled, you can always pass the boot option if absolutely necessary. 1259 1260config RELAY 1261 bool "Kernel->user space relay support (formerly relayfs)" 1262 help 1263 This option enables support for relay interface support in 1264 certain file systems (such as debugfs). 1265 It is designed to provide an efficient mechanism for tools and 1266 facilities to relay large amounts of data from kernel space to 1267 user space. 1268 1269 If unsure, say N. 1270 1271config BLK_DEV_INITRD 1272 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support" 1273 depends on BROKEN || !FRV 1274 help 1275 The initial RAM filesystem is a ramfs which is loaded by the 1276 boot loader (loadlin or lilo) and that is mounted as root 1277 before the normal boot procedure. It is typically used to 1278 load modules needed to mount the "real" root file system, 1279 etc. See <file:Documentation/initrd.txt> for details. 1280 1281 If RAM disk support (BLK_DEV_RAM) is also included, this 1282 also enables initial RAM disk (initrd) support and adds 1283 15 Kbytes (more on some other architectures) to the kernel size. 1284 1285 If unsure say Y. 1286 1287if BLK_DEV_INITRD 1288 1289source "usr/Kconfig" 1290 1291endif 1292 1293config CC_OPTIMIZE_FOR_SIZE 1294 bool "Optimize for size" 1295 help 1296 Enabling this option will pass "-Os" instead of "-O2" to 1297 your compiler resulting in a smaller kernel. 1298 1299 If unsure, say N. 1300 1301config SYSCTL 1302 bool 1303 1304config ANON_INODES 1305 bool 1306 1307config HAVE_UID16 1308 bool 1309 1310config SYSCTL_EXCEPTION_TRACE 1311 bool 1312 help 1313 Enable support for /proc/sys/debug/exception-trace. 1314 1315config SYSCTL_ARCH_UNALIGN_NO_WARN 1316 bool 1317 help 1318 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap 1319 Allows arch to define/use @no_unaligned_warning to possibly warn 1320 about unaligned access emulation going on under the hood. 1321 1322config SYSCTL_ARCH_UNALIGN_ALLOW 1323 bool 1324 help 1325 Enable support for /proc/sys/kernel/unaligned-trap 1326 Allows arches to define/use @unaligned_enabled to runtime toggle 1327 the unaligned access emulation. 1328 see arch/parisc/kernel/unaligned.c for reference 1329 1330config HAVE_PCSPKR_PLATFORM 1331 bool 1332 1333# interpreter that classic socket filters depend on 1334config BPF 1335 bool 1336 1337menuconfig EXPERT 1338 bool "Configure standard kernel features (expert users)" 1339 # Unhide debug options, to make the on-by-default options visible 1340 select DEBUG_KERNEL 1341 help 1342 This option allows certain base kernel options and settings 1343 to be disabled or tweaked. This is for specialized 1344 environments which can tolerate a "non-standard" kernel. 1345 Only use this if you really know what you are doing. 1346 1347config UID16 1348 bool "Enable 16-bit UID system calls" if EXPERT 1349 depends on HAVE_UID16 && MULTIUSER 1350 default y 1351 help 1352 This enables the legacy 16-bit UID syscall wrappers. 1353 1354config MULTIUSER 1355 bool "Multiple users, groups and capabilities support" if EXPERT 1356 default y 1357 help 1358 This option enables support for non-root users, groups and 1359 capabilities. 1360 1361 If you say N here, all processes will run with UID 0, GID 0, and all 1362 possible capabilities. Saying N here also compiles out support for 1363 system calls related to UIDs, GIDs, and capabilities, such as setuid, 1364 setgid, and capset. 1365 1366 If unsure, say Y here. 1367 1368config SGETMASK_SYSCALL 1369 bool "sgetmask/ssetmask syscalls support" if EXPERT 1370 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH 1371 ---help--- 1372 sys_sgetmask and sys_ssetmask are obsolete system calls 1373 no longer supported in libc but still enabled by default in some 1374 architectures. 1375 1376 If unsure, leave the default option here. 1377 1378config SYSFS_SYSCALL 1379 bool "Sysfs syscall support" if EXPERT 1380 default y 1381 ---help--- 1382 sys_sysfs is an obsolete system call no longer supported in libc. 1383 Note that disabling this option is more secure but might break 1384 compatibility with some systems. 1385 1386 If unsure say Y here. 1387 1388config SYSCTL_SYSCALL 1389 bool "Sysctl syscall support" if EXPERT 1390 depends on PROC_SYSCTL 1391 default n 1392 select SYSCTL 1393 ---help--- 1394 sys_sysctl uses binary paths that have been found challenging 1395 to properly maintain and use. The interface in /proc/sys 1396 using paths with ascii names is now the primary path to this 1397 information. 1398 1399 Almost nothing using the binary sysctl interface so if you are 1400 trying to save some space it is probably safe to disable this, 1401 making your kernel marginally smaller. 1402 1403 If unsure say N here. 1404 1405config KALLSYMS 1406 bool "Load all symbols for debugging/ksymoops" if EXPERT 1407 default y 1408 help 1409 Say Y here to let the kernel print out symbolic crash information and 1410 symbolic stack backtraces. This increases the size of the kernel 1411 somewhat, as all symbols have to be loaded into the kernel image. 1412 1413config KALLSYMS_ALL 1414 bool "Include all symbols in kallsyms" 1415 depends on DEBUG_KERNEL && KALLSYMS 1416 help 1417 Normally kallsyms only contains the symbols of functions for nicer 1418 OOPS messages and backtraces (i.e., symbols from the text and inittext 1419 sections). This is sufficient for most cases. And only in very rare 1420 cases (e.g., when a debugger is used) all symbols are required (e.g., 1421 names of variables from the data sections, etc). 1422 1423 This option makes sure that all symbols are loaded into the kernel 1424 image (i.e., symbols from all sections) in cost of increased kernel 1425 size (depending on the kernel configuration, it may be 300KiB or 1426 something like this). 1427 1428 Say N unless you really need all symbols. 1429 1430config PRINTK 1431 default y 1432 bool "Enable support for printk" if EXPERT 1433 select IRQ_WORK 1434 help 1435 This option enables normal printk support. Removing it 1436 eliminates most of the message strings from the kernel image 1437 and makes the kernel more or less silent. As this makes it 1438 very difficult to diagnose system problems, saying N here is 1439 strongly discouraged. 1440 1441config BUG 1442 bool "BUG() support" if EXPERT 1443 default y 1444 help 1445 Disabling this option eliminates support for BUG and WARN, reducing 1446 the size of your kernel image and potentially quietly ignoring 1447 numerous fatal conditions. You should only consider disabling this 1448 option for embedded systems with no facilities for reporting errors. 1449 Just say Y. 1450 1451config ELF_CORE 1452 depends on COREDUMP 1453 default y 1454 bool "Enable ELF core dumps" if EXPERT 1455 help 1456 Enable support for generating core dumps. Disabling saves about 4k. 1457 1458 1459config PCSPKR_PLATFORM 1460 bool "Enable PC-Speaker support" if EXPERT 1461 depends on HAVE_PCSPKR_PLATFORM 1462 select I8253_LOCK 1463 default y 1464 help 1465 This option allows to disable the internal PC-Speaker 1466 support, saving some memory. 1467 1468config BASE_FULL 1469 default y 1470 bool "Enable full-sized data structures for core" if EXPERT 1471 help 1472 Disabling this option reduces the size of miscellaneous core 1473 kernel data structures. This saves memory on small machines, 1474 but may reduce performance. 1475 1476config FUTEX 1477 bool "Enable futex support" if EXPERT 1478 default y 1479 select RT_MUTEXES 1480 help 1481 Disabling this option will cause the kernel to be built without 1482 support for "fast userspace mutexes". The resulting kernel may not 1483 run glibc-based applications correctly. 1484 1485config HAVE_FUTEX_CMPXCHG 1486 bool 1487 depends on FUTEX 1488 help 1489 Architectures should select this if futex_atomic_cmpxchg_inatomic() 1490 is implemented and always working. This removes a couple of runtime 1491 checks. 1492 1493config EPOLL 1494 bool "Enable eventpoll support" if EXPERT 1495 default y 1496 select ANON_INODES 1497 help 1498 Disabling this option will cause the kernel to be built without 1499 support for epoll family of system calls. 1500 1501config SIGNALFD 1502 bool "Enable signalfd() system call" if EXPERT 1503 select ANON_INODES 1504 default y 1505 help 1506 Enable the signalfd() system call that allows to receive signals 1507 on a file descriptor. 1508 1509 If unsure, say Y. 1510 1511config TIMERFD 1512 bool "Enable timerfd() system call" if EXPERT 1513 select ANON_INODES 1514 default y 1515 help 1516 Enable the timerfd() system call that allows to receive timer 1517 events on a file descriptor. 1518 1519 If unsure, say Y. 1520 1521config EVENTFD 1522 bool "Enable eventfd() system call" if EXPERT 1523 select ANON_INODES 1524 default y 1525 help 1526 Enable the eventfd() system call that allows to receive both 1527 kernel notification (ie. KAIO) or userspace notifications. 1528 1529 If unsure, say Y. 1530 1531# syscall, maps, verifier 1532config BPF_SYSCALL 1533 bool "Enable bpf() system call" 1534 select ANON_INODES 1535 select BPF 1536 default n 1537 help 1538 Enable the bpf() system call that allows to manipulate eBPF 1539 programs and maps via file descriptors. 1540 1541config SHMEM 1542 bool "Use full shmem filesystem" if EXPERT 1543 default y 1544 depends on MMU 1545 help 1546 The shmem is an internal filesystem used to manage shared memory. 1547 It is backed by swap and manages resource limits. It is also exported 1548 to userspace as tmpfs if TMPFS is enabled. Disabling this 1549 option replaces shmem and tmpfs with the much simpler ramfs code, 1550 which may be appropriate on small systems without swap. 1551 1552config AIO 1553 bool "Enable AIO support" if EXPERT 1554 default y 1555 help 1556 This option enables POSIX asynchronous I/O which may by used 1557 by some high performance threaded applications. Disabling 1558 this option saves about 7k. 1559 1560config ADVISE_SYSCALLS 1561 bool "Enable madvise/fadvise syscalls" if EXPERT 1562 default y 1563 help 1564 This option enables the madvise and fadvise syscalls, used by 1565 applications to advise the kernel about their future memory or file 1566 usage, improving performance. If building an embedded system where no 1567 applications use these syscalls, you can disable this option to save 1568 space. 1569 1570config PCI_QUIRKS 1571 default y 1572 bool "Enable PCI quirk workarounds" if EXPERT 1573 depends on PCI 1574 help 1575 This enables workarounds for various PCI chipset 1576 bugs/quirks. Disable this only if your target machine is 1577 unaffected by PCI quirks. 1578 1579config EMBEDDED 1580 bool "Embedded system" 1581 option allnoconfig_y 1582 select EXPERT 1583 help 1584 This option should be enabled if compiling the kernel for 1585 an embedded system so certain expert options are available 1586 for configuration. 1587 1588config HAVE_PERF_EVENTS 1589 bool 1590 help 1591 See tools/perf/design.txt for details. 1592 1593config PERF_USE_VMALLOC 1594 bool 1595 help 1596 See tools/perf/design.txt for details 1597 1598menu "Kernel Performance Events And Counters" 1599 1600config PERF_EVENTS 1601 bool "Kernel performance events and counters" 1602 default y if PROFILING 1603 depends on HAVE_PERF_EVENTS 1604 select ANON_INODES 1605 select IRQ_WORK 1606 select SRCU 1607 help 1608 Enable kernel support for various performance events provided 1609 by software and hardware. 1610 1611 Software events are supported either built-in or via the 1612 use of generic tracepoints. 1613 1614 Most modern CPUs support performance events via performance 1615 counter registers. These registers count the number of certain 1616 types of hw events: such as instructions executed, cachemisses 1617 suffered, or branches mis-predicted - without slowing down the 1618 kernel or applications. These registers can also trigger interrupts 1619 when a threshold number of events have passed - and can thus be 1620 used to profile the code that runs on that CPU. 1621 1622 The Linux Performance Event subsystem provides an abstraction of 1623 these software and hardware event capabilities, available via a 1624 system call and used by the "perf" utility in tools/perf/. It 1625 provides per task and per CPU counters, and it provides event 1626 capabilities on top of those. 1627 1628 Say Y if unsure. 1629 1630config DEBUG_PERF_USE_VMALLOC 1631 default n 1632 bool "Debug: use vmalloc to back perf mmap() buffers" 1633 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC 1634 select PERF_USE_VMALLOC 1635 help 1636 Use vmalloc memory to back perf mmap() buffers. 1637 1638 Mostly useful for debugging the vmalloc code on platforms 1639 that don't require it. 1640 1641 Say N if unsure. 1642 1643endmenu 1644 1645config VM_EVENT_COUNTERS 1646 default y 1647 bool "Enable VM event counters for /proc/vmstat" if EXPERT 1648 help 1649 VM event counters are needed for event counts to be shown. 1650 This option allows the disabling of the VM event counters 1651 on EXPERT systems. /proc/vmstat will only show page counts 1652 if VM event counters are disabled. 1653 1654config SLUB_DEBUG 1655 default y 1656 bool "Enable SLUB debugging support" if EXPERT 1657 depends on SLUB && SYSFS 1658 help 1659 SLUB has extensive debug support features. Disabling these can 1660 result in significant savings in code size. This also disables 1661 SLUB sysfs support. /sys/slab will not exist and there will be 1662 no support for cache validation etc. 1663 1664config COMPAT_BRK 1665 bool "Disable heap randomization" 1666 default y 1667 help 1668 Randomizing heap placement makes heap exploits harder, but it 1669 also breaks ancient binaries (including anything libc5 based). 1670 This option changes the bootup default to heap randomization 1671 disabled, and can be overridden at runtime by setting 1672 /proc/sys/kernel/randomize_va_space to 2. 1673 1674 On non-ancient distros (post-2000 ones) N is usually a safe choice. 1675 1676choice 1677 prompt "Choose SLAB allocator" 1678 default SLUB 1679 help 1680 This option allows to select a slab allocator. 1681 1682config SLAB 1683 bool "SLAB" 1684 help 1685 The regular slab allocator that is established and known to work 1686 well in all environments. It organizes cache hot objects in 1687 per cpu and per node queues. 1688 1689config SLUB 1690 bool "SLUB (Unqueued Allocator)" 1691 help 1692 SLUB is a slab allocator that minimizes cache line usage 1693 instead of managing queues of cached objects (SLAB approach). 1694 Per cpu caching is realized using slabs of objects instead 1695 of queues of objects. SLUB can use memory efficiently 1696 and has enhanced diagnostics. SLUB is the default choice for 1697 a slab allocator. 1698 1699config SLOB 1700 depends on EXPERT 1701 bool "SLOB (Simple Allocator)" 1702 help 1703 SLOB replaces the stock allocator with a drastically simpler 1704 allocator. SLOB is generally more space efficient but 1705 does not perform as well on large systems. 1706 1707endchoice 1708 1709config SLUB_CPU_PARTIAL 1710 default y 1711 depends on SLUB && SMP 1712 bool "SLUB per cpu partial cache" 1713 help 1714 Per cpu partial caches accellerate objects allocation and freeing 1715 that is local to a processor at the price of more indeterminism 1716 in the latency of the free. On overflow these caches will be cleared 1717 which requires the taking of locks that may cause latency spikes. 1718 Typically one would choose no for a realtime system. 1719 1720config MMAP_ALLOW_UNINITIALIZED 1721 bool "Allow mmapped anonymous memory to be uninitialized" 1722 depends on EXPERT && !MMU 1723 default n 1724 help 1725 Normally, and according to the Linux spec, anonymous memory obtained 1726 from mmap() has it's contents cleared before it is passed to 1727 userspace. Enabling this config option allows you to request that 1728 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus 1729 providing a huge performance boost. If this option is not enabled, 1730 then the flag will be ignored. 1731 1732 This is taken advantage of by uClibc's malloc(), and also by 1733 ELF-FDPIC binfmt's brk and stack allocator. 1734 1735 Because of the obvious security issues, this option should only be 1736 enabled on embedded devices where you control what is run in 1737 userspace. Since that isn't generally a problem on no-MMU systems, 1738 it is normally safe to say Y here. 1739 1740 See Documentation/nommu-mmap.txt for more information. 1741 1742config SYSTEM_TRUSTED_KEYRING 1743 bool "Provide system-wide ring of trusted keys" 1744 depends on KEYS 1745 help 1746 Provide a system keyring to which trusted keys can be added. Keys in 1747 the keyring are considered to be trusted. Keys may be added at will 1748 by the kernel from compiled-in data and from hardware key stores, but 1749 userspace may only add extra keys if those keys can be verified by 1750 keys already in the keyring. 1751 1752 Keys in this keyring are used by module signature checking. 1753 1754config PROFILING 1755 bool "Profiling support" 1756 help 1757 Say Y here to enable the extended profiling support mechanisms used 1758 by profilers such as OProfile. 1759 1760# 1761# Place an empty function call at each tracepoint site. Can be 1762# dynamically changed for a probe function. 1763# 1764config TRACEPOINTS 1765 bool 1766 1767source "arch/Kconfig" 1768 1769endmenu # General setup 1770 1771config HAVE_GENERIC_DMA_COHERENT 1772 bool 1773 default n 1774 1775config SLABINFO 1776 bool 1777 depends on PROC_FS 1778 depends on SLAB || SLUB_DEBUG 1779 default y 1780 1781config RT_MUTEXES 1782 bool 1783 1784config BASE_SMALL 1785 int 1786 default 0 if BASE_FULL 1787 default 1 if !BASE_FULL 1788 1789menuconfig MODULES 1790 bool "Enable loadable module support" 1791 option modules 1792 help 1793 Kernel modules are small pieces of compiled code which can 1794 be inserted in the running kernel, rather than being 1795 permanently built into the kernel. You use the "modprobe" 1796 tool to add (and sometimes remove) them. If you say Y here, 1797 many parts of the kernel can be built as modules (by 1798 answering M instead of Y where indicated): this is most 1799 useful for infrequently used options which are not required 1800 for booting. For more information, see the man pages for 1801 modprobe, lsmod, modinfo, insmod and rmmod. 1802 1803 If you say Y here, you will need to run "make 1804 modules_install" to put the modules under /lib/modules/ 1805 where modprobe can find them (you may need to be root to do 1806 this). 1807 1808 If unsure, say Y. 1809 1810if MODULES 1811 1812config MODULE_FORCE_LOAD 1813 bool "Forced module loading" 1814 default n 1815 help 1816 Allow loading of modules without version information (ie. modprobe 1817 --force). Forced module loading sets the 'F' (forced) taint flag and 1818 is usually a really bad idea. 1819 1820config MODULE_UNLOAD 1821 bool "Module unloading" 1822 help 1823 Without this option you will not be able to unload any 1824 modules (note that some modules may not be unloadable 1825 anyway), which makes your kernel smaller, faster 1826 and simpler. If unsure, say Y. 1827 1828config MODULE_FORCE_UNLOAD 1829 bool "Forced module unloading" 1830 depends on MODULE_UNLOAD 1831 help 1832 This option allows you to force a module to unload, even if the 1833 kernel believes it is unsafe: the kernel will remove the module 1834 without waiting for anyone to stop using it (using the -f option to 1835 rmmod). This is mainly for kernel developers and desperate users. 1836 If unsure, say N. 1837 1838config MODVERSIONS 1839 bool "Module versioning support" 1840 help 1841 Usually, you have to use modules compiled with your kernel. 1842 Saying Y here makes it sometimes possible to use modules 1843 compiled for different kernels, by adding enough information 1844 to the modules to (hopefully) spot any changes which would 1845 make them incompatible with the kernel you are running. If 1846 unsure, say N. 1847 1848config MODULE_SRCVERSION_ALL 1849 bool "Source checksum for all modules" 1850 help 1851 Modules which contain a MODULE_VERSION get an extra "srcversion" 1852 field inserted into their modinfo section, which contains a 1853 sum of the source files which made it. This helps maintainers 1854 see exactly which source was used to build a module (since 1855 others sometimes change the module source without updating 1856 the version). With this option, such a "srcversion" field 1857 will be created for all modules. If unsure, say N. 1858 1859config MODULE_SIG 1860 bool "Module signature verification" 1861 depends on MODULES 1862 select SYSTEM_TRUSTED_KEYRING 1863 select KEYS 1864 select CRYPTO 1865 select ASYMMETRIC_KEY_TYPE 1866 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE 1867 select PUBLIC_KEY_ALGO_RSA 1868 select ASN1 1869 select OID_REGISTRY 1870 select X509_CERTIFICATE_PARSER 1871 help 1872 Check modules for valid signatures upon load: the signature 1873 is simply appended to the module. For more information see 1874 Documentation/module-signing.txt. 1875 1876 !!!WARNING!!! If you enable this option, you MUST make sure that the 1877 module DOES NOT get stripped after being signed. This includes the 1878 debuginfo strip done by some packagers (such as rpmbuild) and 1879 inclusion into an initramfs that wants the module size reduced. 1880 1881config MODULE_SIG_FORCE 1882 bool "Require modules to be validly signed" 1883 depends on MODULE_SIG 1884 help 1885 Reject unsigned modules or signed modules for which we don't have a 1886 key. Without this, such modules will simply taint the kernel. 1887 1888config MODULE_SIG_ALL 1889 bool "Automatically sign all modules" 1890 default y 1891 depends on MODULE_SIG 1892 help 1893 Sign all modules during make modules_install. Without this option, 1894 modules must be signed manually, using the scripts/sign-file tool. 1895 1896comment "Do not forget to sign required modules with scripts/sign-file" 1897 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL 1898 1899choice 1900 prompt "Which hash algorithm should modules be signed with?" 1901 depends on MODULE_SIG 1902 help 1903 This determines which sort of hashing algorithm will be used during 1904 signature generation. This algorithm _must_ be built into the kernel 1905 directly so that signature verification can take place. It is not 1906 possible to load a signed module containing the algorithm to check 1907 the signature on that module. 1908 1909config MODULE_SIG_SHA1 1910 bool "Sign modules with SHA-1" 1911 select CRYPTO_SHA1 1912 1913config MODULE_SIG_SHA224 1914 bool "Sign modules with SHA-224" 1915 select CRYPTO_SHA256 1916 1917config MODULE_SIG_SHA256 1918 bool "Sign modules with SHA-256" 1919 select CRYPTO_SHA256 1920 1921config MODULE_SIG_SHA384 1922 bool "Sign modules with SHA-384" 1923 select CRYPTO_SHA512 1924 1925config MODULE_SIG_SHA512 1926 bool "Sign modules with SHA-512" 1927 select CRYPTO_SHA512 1928 1929endchoice 1930 1931config MODULE_SIG_HASH 1932 string 1933 depends on MODULE_SIG 1934 default "sha1" if MODULE_SIG_SHA1 1935 default "sha224" if MODULE_SIG_SHA224 1936 default "sha256" if MODULE_SIG_SHA256 1937 default "sha384" if MODULE_SIG_SHA384 1938 default "sha512" if MODULE_SIG_SHA512 1939 1940config MODULE_COMPRESS 1941 bool "Compress modules on installation" 1942 depends on MODULES 1943 help 1944 This option compresses the kernel modules when 'make 1945 modules_install' is run. 1946 1947 The modules will be compressed either using gzip or xz depend on the 1948 choice made in "Compression algorithm". 1949 1950 module-init-tools has support for gzip format while kmod handle gzip 1951 and xz compressed modules. 1952 1953 When a kernel module is installed from outside of the main kernel 1954 source and uses the Kbuild system for installing modules then that 1955 kernel module will also be compressed when it is installed. 1956 1957 This option provides little benefit when the modules are to be used inside 1958 an initrd or initramfs, it generally is more efficient to compress the whole 1959 initrd or initramfs instead. 1960 1961 This is fully compatible with signed modules while the signed module is 1962 compressed. module-init-tools or kmod handles decompression and provide to 1963 other layer the uncompressed but signed payload. 1964 1965choice 1966 prompt "Compression algorithm" 1967 depends on MODULE_COMPRESS 1968 default MODULE_COMPRESS_GZIP 1969 help 1970 This determines which sort of compression will be used during 1971 'make modules_install'. 1972 1973 GZIP (default) and XZ are supported. 1974 1975config MODULE_COMPRESS_GZIP 1976 bool "GZIP" 1977 1978config MODULE_COMPRESS_XZ 1979 bool "XZ" 1980 1981endchoice 1982 1983endif # MODULES 1984 1985config INIT_ALL_POSSIBLE 1986 bool 1987 help 1988 Back when each arch used to define their own cpu_online_mask and 1989 cpu_possible_mask, some of them chose to initialize cpu_possible_mask 1990 with all 1s, and others with all 0s. When they were centralised, 1991 it was better to provide this option than to break all the archs 1992 and have several arch maintainers pursuing me down dark alleys. 1993 1994config STOP_MACHINE 1995 bool 1996 default y 1997 depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU 1998 help 1999 Need stop_machine() primitive. 2000 2001source "block/Kconfig" 2002 2003config PREEMPT_NOTIFIERS 2004 bool 2005 2006config PADATA 2007 depends on SMP 2008 bool 2009 2010# Can be selected by architectures with broken toolchains 2011# that get confused by correct const<->read_only section 2012# mappings 2013config BROKEN_RODATA 2014 bool 2015 2016config ASN1 2017 tristate 2018 help 2019 Build a simple ASN.1 grammar compiler that produces a bytecode output 2020 that can be interpreted by the ASN.1 stream decoder and used to 2021 inform it as to what tags are to be expected in a stream and what 2022 functions to call on what tags. 2023 2024source "kernel/Kconfig.locks" 2025