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