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 help 928 This option adds support for grouping sets of processes together, for 929 use with process control subsystems such as Cpusets, CFS, memory 930 controls or device isolation. 931 See 932 - Documentation/scheduler/sched-design-CFS.txt (CFS) 933 - Documentation/cgroups/ (features for grouping, isolation 934 and resource control) 935 936 Say N if unsure. 937 938if CGROUPS 939 940config CGROUP_DEBUG 941 bool "Example debug cgroup subsystem" 942 default n 943 help 944 This option enables a simple cgroup subsystem that 945 exports useful debugging information about the cgroups 946 framework. 947 948 Say N if unsure. 949 950config CGROUP_FREEZER 951 bool "Freezer cgroup subsystem" 952 help 953 Provides a way to freeze and unfreeze all tasks in a 954 cgroup. 955 956config CGROUP_DEVICE 957 bool "Device controller for cgroups" 958 help 959 Provides a cgroup implementing whitelists for devices which 960 a process in the cgroup can mknod or open. 961 962config CPUSETS 963 bool "Cpuset support" 964 help 965 This option will let you create and manage CPUSETs which 966 allow dynamically partitioning a system into sets of CPUs and 967 Memory Nodes and assigning tasks to run only within those sets. 968 This is primarily useful on large SMP or NUMA systems. 969 970 Say N if unsure. 971 972config PROC_PID_CPUSET 973 bool "Include legacy /proc/<pid>/cpuset file" 974 depends on CPUSETS 975 default y 976 977config CGROUP_CPUACCT 978 bool "Simple CPU accounting cgroup subsystem" 979 help 980 Provides a simple Resource Controller for monitoring the 981 total CPU consumed by the tasks in a cgroup. 982 983config PAGE_COUNTER 984 bool 985 986config MEMCG 987 bool "Memory Resource Controller for Control Groups" 988 select PAGE_COUNTER 989 select EVENTFD 990 help 991 Provides a memory resource controller that manages both anonymous 992 memory and page cache. (See Documentation/cgroups/memory.txt) 993 994config MEMCG_SWAP 995 bool "Memory Resource Controller Swap Extension" 996 depends on MEMCG && SWAP 997 help 998 Add swap management feature to memory resource controller. When you 999 enable this, you can limit mem+swap usage per cgroup. In other words, 1000 when you disable this, memory resource controller has no cares to 1001 usage of swap...a process can exhaust all of the swap. This extension 1002 is useful when you want to avoid exhaustion swap but this itself 1003 adds more overheads and consumes memory for remembering information. 1004 Especially if you use 32bit system or small memory system, please 1005 be careful about enabling this. When memory resource controller 1006 is disabled by boot option, this will be automatically disabled and 1007 there will be no overhead from this. Even when you set this config=y, 1008 if boot option "swapaccount=0" is set, swap will not be accounted. 1009 Now, memory usage of swap_cgroup is 2 bytes per entry. If swap page 1010 size is 4096bytes, 512k per 1Gbytes of swap. 1011config MEMCG_SWAP_ENABLED 1012 bool "Memory Resource Controller Swap Extension enabled by default" 1013 depends on MEMCG_SWAP 1014 default y 1015 help 1016 Memory Resource Controller Swap Extension comes with its price in 1017 a bigger memory consumption. General purpose distribution kernels 1018 which want to enable the feature but keep it disabled by default 1019 and let the user enable it by swapaccount=1 boot command line 1020 parameter should have this option unselected. 1021 For those who want to have the feature enabled by default should 1022 select this option (if, for some reason, they need to disable it 1023 then swapaccount=0 does the trick). 1024config MEMCG_KMEM 1025 bool "Memory Resource Controller Kernel Memory accounting" 1026 depends on MEMCG 1027 depends on SLUB || SLAB 1028 help 1029 The Kernel Memory extension for Memory Resource Controller can limit 1030 the amount of memory used by kernel objects in the system. Those are 1031 fundamentally different from the entities handled by the standard 1032 Memory Controller, which are page-based, and can be swapped. Users of 1033 the kmem extension can use it to guarantee that no group of processes 1034 will ever exhaust kernel resources alone. 1035 1036config CGROUP_HUGETLB 1037 bool "HugeTLB Resource Controller for Control Groups" 1038 depends on HUGETLB_PAGE 1039 select PAGE_COUNTER 1040 default n 1041 help 1042 Provides a cgroup Resource Controller for HugeTLB pages. 1043 When you enable this, you can put a per cgroup limit on HugeTLB usage. 1044 The limit is enforced during page fault. Since HugeTLB doesn't 1045 support page reclaim, enforcing the limit at page fault time implies 1046 that, the application will get SIGBUS signal if it tries to access 1047 HugeTLB pages beyond its limit. This requires the application to know 1048 beforehand how much HugeTLB pages it would require for its use. The 1049 control group is tracked in the third page lru pointer. This means 1050 that we cannot use the controller with huge page less than 3 pages. 1051 1052config CGROUP_PERF 1053 bool "Enable perf_event per-cpu per-container group (cgroup) monitoring" 1054 depends on PERF_EVENTS && CGROUPS 1055 help 1056 This option extends the per-cpu mode to restrict monitoring to 1057 threads which belong to the cgroup specified and run on the 1058 designated cpu. 1059 1060 Say N if unsure. 1061 1062menuconfig CGROUP_SCHED 1063 bool "Group CPU scheduler" 1064 default n 1065 help 1066 This feature lets CPU scheduler recognize task groups and control CPU 1067 bandwidth allocation to such task groups. It uses cgroups to group 1068 tasks. 1069 1070if CGROUP_SCHED 1071config FAIR_GROUP_SCHED 1072 bool "Group scheduling for SCHED_OTHER" 1073 depends on CGROUP_SCHED 1074 default CGROUP_SCHED 1075 1076config CFS_BANDWIDTH 1077 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED" 1078 depends on FAIR_GROUP_SCHED 1079 default n 1080 help 1081 This option allows users to define CPU bandwidth rates (limits) for 1082 tasks running within the fair group scheduler. Groups with no limit 1083 set are considered to be unconstrained and will run with no 1084 restriction. 1085 See tip/Documentation/scheduler/sched-bwc.txt for more information. 1086 1087config RT_GROUP_SCHED 1088 bool "Group scheduling for SCHED_RR/FIFO" 1089 depends on CGROUP_SCHED 1090 default n 1091 help 1092 This feature lets you explicitly allocate real CPU bandwidth 1093 to task groups. If enabled, it will also make it impossible to 1094 schedule realtime tasks for non-root users until you allocate 1095 realtime bandwidth for them. 1096 See Documentation/scheduler/sched-rt-group.txt for more information. 1097 1098endif #CGROUP_SCHED 1099 1100config BLK_CGROUP 1101 bool "Block IO controller" 1102 depends on BLOCK 1103 default n 1104 ---help--- 1105 Generic block IO controller cgroup interface. This is the common 1106 cgroup interface which should be used by various IO controlling 1107 policies. 1108 1109 Currently, CFQ IO scheduler uses it to recognize task groups and 1110 control disk bandwidth allocation (proportional time slice allocation) 1111 to such task groups. It is also used by bio throttling logic in 1112 block layer to implement upper limit in IO rates on a device. 1113 1114 This option only enables generic Block IO controller infrastructure. 1115 One needs to also enable actual IO controlling logic/policy. For 1116 enabling proportional weight division of disk bandwidth in CFQ, set 1117 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set 1118 CONFIG_BLK_DEV_THROTTLING=y. 1119 1120 See Documentation/cgroups/blkio-controller.txt for more information. 1121 1122config DEBUG_BLK_CGROUP 1123 bool "Enable Block IO controller debugging" 1124 depends on BLK_CGROUP 1125 default n 1126 ---help--- 1127 Enable some debugging help. Currently it exports additional stat 1128 files in a cgroup which can be useful for debugging. 1129 1130endif # CGROUPS 1131 1132config CHECKPOINT_RESTORE 1133 bool "Checkpoint/restore support" if EXPERT 1134 default n 1135 help 1136 Enables additional kernel features in a sake of checkpoint/restore. 1137 In particular it adds auxiliary prctl codes to setup process text, 1138 data and heap segment sizes, and a few additional /proc filesystem 1139 entries. 1140 1141 If unsure, say N here. 1142 1143menuconfig NAMESPACES 1144 bool "Namespaces support" if EXPERT 1145 depends on MULTIUSER 1146 default !EXPERT 1147 help 1148 Provides the way to make tasks work with different objects using 1149 the same id. For example same IPC id may refer to different objects 1150 or same user id or pid may refer to different tasks when used in 1151 different namespaces. 1152 1153if NAMESPACES 1154 1155config UTS_NS 1156 bool "UTS namespace" 1157 default y 1158 help 1159 In this namespace tasks see different info provided with the 1160 uname() system call 1161 1162config IPC_NS 1163 bool "IPC namespace" 1164 depends on (SYSVIPC || POSIX_MQUEUE) 1165 default y 1166 help 1167 In this namespace tasks work with IPC ids which correspond to 1168 different IPC objects in different namespaces. 1169 1170config USER_NS 1171 bool "User namespace" 1172 default n 1173 help 1174 This allows containers, i.e. vservers, to use user namespaces 1175 to provide different user info for different servers. 1176 1177 When user namespaces are enabled in the kernel it is 1178 recommended that the MEMCG and MEMCG_KMEM options also be 1179 enabled and that user-space use the memory control groups to 1180 limit the amount of memory a memory unprivileged users can 1181 use. 1182 1183 If unsure, say N. 1184 1185config PID_NS 1186 bool "PID Namespaces" 1187 default y 1188 help 1189 Support process id namespaces. This allows having multiple 1190 processes with the same pid as long as they are in different 1191 pid namespaces. This is a building block of containers. 1192 1193config NET_NS 1194 bool "Network namespace" 1195 depends on NET 1196 default y 1197 help 1198 Allow user space to create what appear to be multiple instances 1199 of the network stack. 1200 1201endif # NAMESPACES 1202 1203config SCHED_AUTOGROUP 1204 bool "Automatic process group scheduling" 1205 select CGROUPS 1206 select CGROUP_SCHED 1207 select FAIR_GROUP_SCHED 1208 help 1209 This option optimizes the scheduler for common desktop workloads by 1210 automatically creating and populating task groups. This separation 1211 of workloads isolates aggressive CPU burners (like build jobs) from 1212 desktop applications. Task group autogeneration is currently based 1213 upon task session. 1214 1215config SYSFS_DEPRECATED 1216 bool "Enable deprecated sysfs features to support old userspace tools" 1217 depends on SYSFS 1218 default n 1219 help 1220 This option adds code that switches the layout of the "block" class 1221 devices, to not show up in /sys/class/block/, but only in 1222 /sys/block/. 1223 1224 This switch is only active when the sysfs.deprecated=1 boot option is 1225 passed or the SYSFS_DEPRECATED_V2 option is set. 1226 1227 This option allows new kernels to run on old distributions and tools, 1228 which might get confused by /sys/class/block/. Since 2007/2008 all 1229 major distributions and tools handle this just fine. 1230 1231 Recent distributions and userspace tools after 2009/2010 depend on 1232 the existence of /sys/class/block/, and will not work with this 1233 option enabled. 1234 1235 Only if you are using a new kernel on an old distribution, you might 1236 need to say Y here. 1237 1238config SYSFS_DEPRECATED_V2 1239 bool "Enable deprecated sysfs features by default" 1240 default n 1241 depends on SYSFS 1242 depends on SYSFS_DEPRECATED 1243 help 1244 Enable deprecated sysfs by default. 1245 1246 See the CONFIG_SYSFS_DEPRECATED option for more details about this 1247 option. 1248 1249 Only if you are using a new kernel on an old distribution, you might 1250 need to say Y here. Even then, odds are you would not need it 1251 enabled, you can always pass the boot option if absolutely necessary. 1252 1253config RELAY 1254 bool "Kernel->user space relay support (formerly relayfs)" 1255 help 1256 This option enables support for relay interface support in 1257 certain file systems (such as debugfs). 1258 It is designed to provide an efficient mechanism for tools and 1259 facilities to relay large amounts of data from kernel space to 1260 user space. 1261 1262 If unsure, say N. 1263 1264config BLK_DEV_INITRD 1265 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support" 1266 depends on BROKEN || !FRV 1267 help 1268 The initial RAM filesystem is a ramfs which is loaded by the 1269 boot loader (loadlin or lilo) and that is mounted as root 1270 before the normal boot procedure. It is typically used to 1271 load modules needed to mount the "real" root file system, 1272 etc. See <file:Documentation/initrd.txt> for details. 1273 1274 If RAM disk support (BLK_DEV_RAM) is also included, this 1275 also enables initial RAM disk (initrd) support and adds 1276 15 Kbytes (more on some other architectures) to the kernel size. 1277 1278 If unsure say Y. 1279 1280if BLK_DEV_INITRD 1281 1282source "usr/Kconfig" 1283 1284endif 1285 1286config CC_OPTIMIZE_FOR_SIZE 1287 bool "Optimize for size" 1288 help 1289 Enabling this option will pass "-Os" instead of "-O2" to 1290 your compiler resulting in a smaller kernel. 1291 1292 If unsure, say N. 1293 1294config SYSCTL 1295 bool 1296 1297config ANON_INODES 1298 bool 1299 1300config HAVE_UID16 1301 bool 1302 1303config SYSCTL_EXCEPTION_TRACE 1304 bool 1305 help 1306 Enable support for /proc/sys/debug/exception-trace. 1307 1308config SYSCTL_ARCH_UNALIGN_NO_WARN 1309 bool 1310 help 1311 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap 1312 Allows arch to define/use @no_unaligned_warning to possibly warn 1313 about unaligned access emulation going on under the hood. 1314 1315config SYSCTL_ARCH_UNALIGN_ALLOW 1316 bool 1317 help 1318 Enable support for /proc/sys/kernel/unaligned-trap 1319 Allows arches to define/use @unaligned_enabled to runtime toggle 1320 the unaligned access emulation. 1321 see arch/parisc/kernel/unaligned.c for reference 1322 1323config HAVE_PCSPKR_PLATFORM 1324 bool 1325 1326# interpreter that classic socket filters depend on 1327config BPF 1328 bool 1329 1330menuconfig EXPERT 1331 bool "Configure standard kernel features (expert users)" 1332 # Unhide debug options, to make the on-by-default options visible 1333 select DEBUG_KERNEL 1334 help 1335 This option allows certain base kernel options and settings 1336 to be disabled or tweaked. This is for specialized 1337 environments which can tolerate a "non-standard" kernel. 1338 Only use this if you really know what you are doing. 1339 1340config UID16 1341 bool "Enable 16-bit UID system calls" if EXPERT 1342 depends on HAVE_UID16 && MULTIUSER 1343 default y 1344 help 1345 This enables the legacy 16-bit UID syscall wrappers. 1346 1347config MULTIUSER 1348 bool "Multiple users, groups and capabilities support" if EXPERT 1349 default y 1350 help 1351 This option enables support for non-root users, groups and 1352 capabilities. 1353 1354 If you say N here, all processes will run with UID 0, GID 0, and all 1355 possible capabilities. Saying N here also compiles out support for 1356 system calls related to UIDs, GIDs, and capabilities, such as setuid, 1357 setgid, and capset. 1358 1359 If unsure, say Y here. 1360 1361config SGETMASK_SYSCALL 1362 bool "sgetmask/ssetmask syscalls support" if EXPERT 1363 def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH 1364 ---help--- 1365 sys_sgetmask and sys_ssetmask are obsolete system calls 1366 no longer supported in libc but still enabled by default in some 1367 architectures. 1368 1369 If unsure, leave the default option here. 1370 1371config SYSFS_SYSCALL 1372 bool "Sysfs syscall support" if EXPERT 1373 default y 1374 ---help--- 1375 sys_sysfs is an obsolete system call no longer supported in libc. 1376 Note that disabling this option is more secure but might break 1377 compatibility with some systems. 1378 1379 If unsure say Y here. 1380 1381config SYSCTL_SYSCALL 1382 bool "Sysctl syscall support" if EXPERT 1383 depends on PROC_SYSCTL 1384 default n 1385 select SYSCTL 1386 ---help--- 1387 sys_sysctl uses binary paths that have been found challenging 1388 to properly maintain and use. The interface in /proc/sys 1389 using paths with ascii names is now the primary path to this 1390 information. 1391 1392 Almost nothing using the binary sysctl interface so if you are 1393 trying to save some space it is probably safe to disable this, 1394 making your kernel marginally smaller. 1395 1396 If unsure say N here. 1397 1398config KALLSYMS 1399 bool "Load all symbols for debugging/ksymoops" if EXPERT 1400 default y 1401 help 1402 Say Y here to let the kernel print out symbolic crash information and 1403 symbolic stack backtraces. This increases the size of the kernel 1404 somewhat, as all symbols have to be loaded into the kernel image. 1405 1406config KALLSYMS_ALL 1407 bool "Include all symbols in kallsyms" 1408 depends on DEBUG_KERNEL && KALLSYMS 1409 help 1410 Normally kallsyms only contains the symbols of functions for nicer 1411 OOPS messages and backtraces (i.e., symbols from the text and inittext 1412 sections). This is sufficient for most cases. And only in very rare 1413 cases (e.g., when a debugger is used) all symbols are required (e.g., 1414 names of variables from the data sections, etc). 1415 1416 This option makes sure that all symbols are loaded into the kernel 1417 image (i.e., symbols from all sections) in cost of increased kernel 1418 size (depending on the kernel configuration, it may be 300KiB or 1419 something like this). 1420 1421 Say N unless you really need all symbols. 1422 1423config PRINTK 1424 default y 1425 bool "Enable support for printk" if EXPERT 1426 select IRQ_WORK 1427 help 1428 This option enables normal printk support. Removing it 1429 eliminates most of the message strings from the kernel image 1430 and makes the kernel more or less silent. As this makes it 1431 very difficult to diagnose system problems, saying N here is 1432 strongly discouraged. 1433 1434config BUG 1435 bool "BUG() support" if EXPERT 1436 default y 1437 help 1438 Disabling this option eliminates support for BUG and WARN, reducing 1439 the size of your kernel image and potentially quietly ignoring 1440 numerous fatal conditions. You should only consider disabling this 1441 option for embedded systems with no facilities for reporting errors. 1442 Just say Y. 1443 1444config ELF_CORE 1445 depends on COREDUMP 1446 default y 1447 bool "Enable ELF core dumps" if EXPERT 1448 help 1449 Enable support for generating core dumps. Disabling saves about 4k. 1450 1451 1452config PCSPKR_PLATFORM 1453 bool "Enable PC-Speaker support" if EXPERT 1454 depends on HAVE_PCSPKR_PLATFORM 1455 select I8253_LOCK 1456 default y 1457 help 1458 This option allows to disable the internal PC-Speaker 1459 support, saving some memory. 1460 1461config BASE_FULL 1462 default y 1463 bool "Enable full-sized data structures for core" if EXPERT 1464 help 1465 Disabling this option reduces the size of miscellaneous core 1466 kernel data structures. This saves memory on small machines, 1467 but may reduce performance. 1468 1469config FUTEX 1470 bool "Enable futex support" if EXPERT 1471 default y 1472 select RT_MUTEXES 1473 help 1474 Disabling this option will cause the kernel to be built without 1475 support for "fast userspace mutexes". The resulting kernel may not 1476 run glibc-based applications correctly. 1477 1478config HAVE_FUTEX_CMPXCHG 1479 bool 1480 depends on FUTEX 1481 help 1482 Architectures should select this if futex_atomic_cmpxchg_inatomic() 1483 is implemented and always working. This removes a couple of runtime 1484 checks. 1485 1486config EPOLL 1487 bool "Enable eventpoll support" if EXPERT 1488 default y 1489 select ANON_INODES 1490 help 1491 Disabling this option will cause the kernel to be built without 1492 support for epoll family of system calls. 1493 1494config SIGNALFD 1495 bool "Enable signalfd() system call" if EXPERT 1496 select ANON_INODES 1497 default y 1498 help 1499 Enable the signalfd() system call that allows to receive signals 1500 on a file descriptor. 1501 1502 If unsure, say Y. 1503 1504config TIMERFD 1505 bool "Enable timerfd() system call" if EXPERT 1506 select ANON_INODES 1507 default y 1508 help 1509 Enable the timerfd() system call that allows to receive timer 1510 events on a file descriptor. 1511 1512 If unsure, say Y. 1513 1514config EVENTFD 1515 bool "Enable eventfd() system call" if EXPERT 1516 select ANON_INODES 1517 default y 1518 help 1519 Enable the eventfd() system call that allows to receive both 1520 kernel notification (ie. KAIO) or userspace notifications. 1521 1522 If unsure, say Y. 1523 1524# syscall, maps, verifier 1525config BPF_SYSCALL 1526 bool "Enable bpf() system call" 1527 select ANON_INODES 1528 select BPF 1529 default n 1530 help 1531 Enable the bpf() system call that allows to manipulate eBPF 1532 programs and maps via file descriptors. 1533 1534config SHMEM 1535 bool "Use full shmem filesystem" if EXPERT 1536 default y 1537 depends on MMU 1538 help 1539 The shmem is an internal filesystem used to manage shared memory. 1540 It is backed by swap and manages resource limits. It is also exported 1541 to userspace as tmpfs if TMPFS is enabled. Disabling this 1542 option replaces shmem and tmpfs with the much simpler ramfs code, 1543 which may be appropriate on small systems without swap. 1544 1545config AIO 1546 bool "Enable AIO support" if EXPERT 1547 default y 1548 help 1549 This option enables POSIX asynchronous I/O which may by used 1550 by some high performance threaded applications. Disabling 1551 this option saves about 7k. 1552 1553config ADVISE_SYSCALLS 1554 bool "Enable madvise/fadvise syscalls" if EXPERT 1555 default y 1556 help 1557 This option enables the madvise and fadvise syscalls, used by 1558 applications to advise the kernel about their future memory or file 1559 usage, improving performance. If building an embedded system where no 1560 applications use these syscalls, you can disable this option to save 1561 space. 1562 1563config PCI_QUIRKS 1564 default y 1565 bool "Enable PCI quirk workarounds" if EXPERT 1566 depends on PCI 1567 help 1568 This enables workarounds for various PCI chipset 1569 bugs/quirks. Disable this only if your target machine is 1570 unaffected by PCI quirks. 1571 1572config EMBEDDED 1573 bool "Embedded system" 1574 option allnoconfig_y 1575 select EXPERT 1576 help 1577 This option should be enabled if compiling the kernel for 1578 an embedded system so certain expert options are available 1579 for configuration. 1580 1581config HAVE_PERF_EVENTS 1582 bool 1583 help 1584 See tools/perf/design.txt for details. 1585 1586config PERF_USE_VMALLOC 1587 bool 1588 help 1589 See tools/perf/design.txt for details 1590 1591menu "Kernel Performance Events And Counters" 1592 1593config PERF_EVENTS 1594 bool "Kernel performance events and counters" 1595 default y if PROFILING 1596 depends on HAVE_PERF_EVENTS 1597 select ANON_INODES 1598 select IRQ_WORK 1599 select SRCU 1600 help 1601 Enable kernel support for various performance events provided 1602 by software and hardware. 1603 1604 Software events are supported either built-in or via the 1605 use of generic tracepoints. 1606 1607 Most modern CPUs support performance events via performance 1608 counter registers. These registers count the number of certain 1609 types of hw events: such as instructions executed, cachemisses 1610 suffered, or branches mis-predicted - without slowing down the 1611 kernel or applications. These registers can also trigger interrupts 1612 when a threshold number of events have passed - and can thus be 1613 used to profile the code that runs on that CPU. 1614 1615 The Linux Performance Event subsystem provides an abstraction of 1616 these software and hardware event capabilities, available via a 1617 system call and used by the "perf" utility in tools/perf/. It 1618 provides per task and per CPU counters, and it provides event 1619 capabilities on top of those. 1620 1621 Say Y if unsure. 1622 1623config DEBUG_PERF_USE_VMALLOC 1624 default n 1625 bool "Debug: use vmalloc to back perf mmap() buffers" 1626 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC 1627 select PERF_USE_VMALLOC 1628 help 1629 Use vmalloc memory to back perf mmap() buffers. 1630 1631 Mostly useful for debugging the vmalloc code on platforms 1632 that don't require it. 1633 1634 Say N if unsure. 1635 1636endmenu 1637 1638config VM_EVENT_COUNTERS 1639 default y 1640 bool "Enable VM event counters for /proc/vmstat" if EXPERT 1641 help 1642 VM event counters are needed for event counts to be shown. 1643 This option allows the disabling of the VM event counters 1644 on EXPERT systems. /proc/vmstat will only show page counts 1645 if VM event counters are disabled. 1646 1647config SLUB_DEBUG 1648 default y 1649 bool "Enable SLUB debugging support" if EXPERT 1650 depends on SLUB && SYSFS 1651 help 1652 SLUB has extensive debug support features. Disabling these can 1653 result in significant savings in code size. This also disables 1654 SLUB sysfs support. /sys/slab will not exist and there will be 1655 no support for cache validation etc. 1656 1657config COMPAT_BRK 1658 bool "Disable heap randomization" 1659 default y 1660 help 1661 Randomizing heap placement makes heap exploits harder, but it 1662 also breaks ancient binaries (including anything libc5 based). 1663 This option changes the bootup default to heap randomization 1664 disabled, and can be overridden at runtime by setting 1665 /proc/sys/kernel/randomize_va_space to 2. 1666 1667 On non-ancient distros (post-2000 ones) N is usually a safe choice. 1668 1669choice 1670 prompt "Choose SLAB allocator" 1671 default SLUB 1672 help 1673 This option allows to select a slab allocator. 1674 1675config SLAB 1676 bool "SLAB" 1677 help 1678 The regular slab allocator that is established and known to work 1679 well in all environments. It organizes cache hot objects in 1680 per cpu and per node queues. 1681 1682config SLUB 1683 bool "SLUB (Unqueued Allocator)" 1684 help 1685 SLUB is a slab allocator that minimizes cache line usage 1686 instead of managing queues of cached objects (SLAB approach). 1687 Per cpu caching is realized using slabs of objects instead 1688 of queues of objects. SLUB can use memory efficiently 1689 and has enhanced diagnostics. SLUB is the default choice for 1690 a slab allocator. 1691 1692config SLOB 1693 depends on EXPERT 1694 bool "SLOB (Simple Allocator)" 1695 help 1696 SLOB replaces the stock allocator with a drastically simpler 1697 allocator. SLOB is generally more space efficient but 1698 does not perform as well on large systems. 1699 1700endchoice 1701 1702config SLUB_CPU_PARTIAL 1703 default y 1704 depends on SLUB && SMP 1705 bool "SLUB per cpu partial cache" 1706 help 1707 Per cpu partial caches accellerate objects allocation and freeing 1708 that is local to a processor at the price of more indeterminism 1709 in the latency of the free. On overflow these caches will be cleared 1710 which requires the taking of locks that may cause latency spikes. 1711 Typically one would choose no for a realtime system. 1712 1713config MMAP_ALLOW_UNINITIALIZED 1714 bool "Allow mmapped anonymous memory to be uninitialized" 1715 depends on EXPERT && !MMU 1716 default n 1717 help 1718 Normally, and according to the Linux spec, anonymous memory obtained 1719 from mmap() has it's contents cleared before it is passed to 1720 userspace. Enabling this config option allows you to request that 1721 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus 1722 providing a huge performance boost. If this option is not enabled, 1723 then the flag will be ignored. 1724 1725 This is taken advantage of by uClibc's malloc(), and also by 1726 ELF-FDPIC binfmt's brk and stack allocator. 1727 1728 Because of the obvious security issues, this option should only be 1729 enabled on embedded devices where you control what is run in 1730 userspace. Since that isn't generally a problem on no-MMU systems, 1731 it is normally safe to say Y here. 1732 1733 See Documentation/nommu-mmap.txt for more information. 1734 1735config SYSTEM_TRUSTED_KEYRING 1736 bool "Provide system-wide ring of trusted keys" 1737 depends on KEYS 1738 help 1739 Provide a system keyring to which trusted keys can be added. Keys in 1740 the keyring are considered to be trusted. Keys may be added at will 1741 by the kernel from compiled-in data and from hardware key stores, but 1742 userspace may only add extra keys if those keys can be verified by 1743 keys already in the keyring. 1744 1745 Keys in this keyring are used by module signature checking. 1746 1747config PROFILING 1748 bool "Profiling support" 1749 help 1750 Say Y here to enable the extended profiling support mechanisms used 1751 by profilers such as OProfile. 1752 1753# 1754# Place an empty function call at each tracepoint site. Can be 1755# dynamically changed for a probe function. 1756# 1757config TRACEPOINTS 1758 bool 1759 1760source "arch/Kconfig" 1761 1762endmenu # General setup 1763 1764config HAVE_GENERIC_DMA_COHERENT 1765 bool 1766 default n 1767 1768config SLABINFO 1769 bool 1770 depends on PROC_FS 1771 depends on SLAB || SLUB_DEBUG 1772 default y 1773 1774config RT_MUTEXES 1775 bool 1776 1777config BASE_SMALL 1778 int 1779 default 0 if BASE_FULL 1780 default 1 if !BASE_FULL 1781 1782menuconfig MODULES 1783 bool "Enable loadable module support" 1784 option modules 1785 help 1786 Kernel modules are small pieces of compiled code which can 1787 be inserted in the running kernel, rather than being 1788 permanently built into the kernel. You use the "modprobe" 1789 tool to add (and sometimes remove) them. If you say Y here, 1790 many parts of the kernel can be built as modules (by 1791 answering M instead of Y where indicated): this is most 1792 useful for infrequently used options which are not required 1793 for booting. For more information, see the man pages for 1794 modprobe, lsmod, modinfo, insmod and rmmod. 1795 1796 If you say Y here, you will need to run "make 1797 modules_install" to put the modules under /lib/modules/ 1798 where modprobe can find them (you may need to be root to do 1799 this). 1800 1801 If unsure, say Y. 1802 1803if MODULES 1804 1805config MODULE_FORCE_LOAD 1806 bool "Forced module loading" 1807 default n 1808 help 1809 Allow loading of modules without version information (ie. modprobe 1810 --force). Forced module loading sets the 'F' (forced) taint flag and 1811 is usually a really bad idea. 1812 1813config MODULE_UNLOAD 1814 bool "Module unloading" 1815 help 1816 Without this option you will not be able to unload any 1817 modules (note that some modules may not be unloadable 1818 anyway), which makes your kernel smaller, faster 1819 and simpler. If unsure, say Y. 1820 1821config MODULE_FORCE_UNLOAD 1822 bool "Forced module unloading" 1823 depends on MODULE_UNLOAD 1824 help 1825 This option allows you to force a module to unload, even if the 1826 kernel believes it is unsafe: the kernel will remove the module 1827 without waiting for anyone to stop using it (using the -f option to 1828 rmmod). This is mainly for kernel developers and desperate users. 1829 If unsure, say N. 1830 1831config MODVERSIONS 1832 bool "Module versioning support" 1833 help 1834 Usually, you have to use modules compiled with your kernel. 1835 Saying Y here makes it sometimes possible to use modules 1836 compiled for different kernels, by adding enough information 1837 to the modules to (hopefully) spot any changes which would 1838 make them incompatible with the kernel you are running. If 1839 unsure, say N. 1840 1841config MODULE_SRCVERSION_ALL 1842 bool "Source checksum for all modules" 1843 help 1844 Modules which contain a MODULE_VERSION get an extra "srcversion" 1845 field inserted into their modinfo section, which contains a 1846 sum of the source files which made it. This helps maintainers 1847 see exactly which source was used to build a module (since 1848 others sometimes change the module source without updating 1849 the version). With this option, such a "srcversion" field 1850 will be created for all modules. If unsure, say N. 1851 1852config MODULE_SIG 1853 bool "Module signature verification" 1854 depends on MODULES 1855 select SYSTEM_TRUSTED_KEYRING 1856 select KEYS 1857 select CRYPTO 1858 select ASYMMETRIC_KEY_TYPE 1859 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE 1860 select PUBLIC_KEY_ALGO_RSA 1861 select ASN1 1862 select OID_REGISTRY 1863 select X509_CERTIFICATE_PARSER 1864 help 1865 Check modules for valid signatures upon load: the signature 1866 is simply appended to the module. For more information see 1867 Documentation/module-signing.txt. 1868 1869 !!!WARNING!!! If you enable this option, you MUST make sure that the 1870 module DOES NOT get stripped after being signed. This includes the 1871 debuginfo strip done by some packagers (such as rpmbuild) and 1872 inclusion into an initramfs that wants the module size reduced. 1873 1874config MODULE_SIG_FORCE 1875 bool "Require modules to be validly signed" 1876 depends on MODULE_SIG 1877 help 1878 Reject unsigned modules or signed modules for which we don't have a 1879 key. Without this, such modules will simply taint the kernel. 1880 1881config MODULE_SIG_ALL 1882 bool "Automatically sign all modules" 1883 default y 1884 depends on MODULE_SIG 1885 help 1886 Sign all modules during make modules_install. Without this option, 1887 modules must be signed manually, using the scripts/sign-file tool. 1888 1889comment "Do not forget to sign required modules with scripts/sign-file" 1890 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL 1891 1892choice 1893 prompt "Which hash algorithm should modules be signed with?" 1894 depends on MODULE_SIG 1895 help 1896 This determines which sort of hashing algorithm will be used during 1897 signature generation. This algorithm _must_ be built into the kernel 1898 directly so that signature verification can take place. It is not 1899 possible to load a signed module containing the algorithm to check 1900 the signature on that module. 1901 1902config MODULE_SIG_SHA1 1903 bool "Sign modules with SHA-1" 1904 select CRYPTO_SHA1 1905 1906config MODULE_SIG_SHA224 1907 bool "Sign modules with SHA-224" 1908 select CRYPTO_SHA256 1909 1910config MODULE_SIG_SHA256 1911 bool "Sign modules with SHA-256" 1912 select CRYPTO_SHA256 1913 1914config MODULE_SIG_SHA384 1915 bool "Sign modules with SHA-384" 1916 select CRYPTO_SHA512 1917 1918config MODULE_SIG_SHA512 1919 bool "Sign modules with SHA-512" 1920 select CRYPTO_SHA512 1921 1922endchoice 1923 1924config MODULE_SIG_HASH 1925 string 1926 depends on MODULE_SIG 1927 default "sha1" if MODULE_SIG_SHA1 1928 default "sha224" if MODULE_SIG_SHA224 1929 default "sha256" if MODULE_SIG_SHA256 1930 default "sha384" if MODULE_SIG_SHA384 1931 default "sha512" if MODULE_SIG_SHA512 1932 1933config MODULE_COMPRESS 1934 bool "Compress modules on installation" 1935 depends on MODULES 1936 help 1937 This option compresses the kernel modules when 'make 1938 modules_install' is run. 1939 1940 The modules will be compressed either using gzip or xz depend on the 1941 choice made in "Compression algorithm". 1942 1943 module-init-tools has support for gzip format while kmod handle gzip 1944 and xz compressed modules. 1945 1946 When a kernel module is installed from outside of the main kernel 1947 source and uses the Kbuild system for installing modules then that 1948 kernel module will also be compressed when it is installed. 1949 1950 This option provides little benefit when the modules are to be used inside 1951 an initrd or initramfs, it generally is more efficient to compress the whole 1952 initrd or initramfs instead. 1953 1954 This is fully compatible with signed modules while the signed module is 1955 compressed. module-init-tools or kmod handles decompression and provide to 1956 other layer the uncompressed but signed payload. 1957 1958choice 1959 prompt "Compression algorithm" 1960 depends on MODULE_COMPRESS 1961 default MODULE_COMPRESS_GZIP 1962 help 1963 This determines which sort of compression will be used during 1964 'make modules_install'. 1965 1966 GZIP (default) and XZ are supported. 1967 1968config MODULE_COMPRESS_GZIP 1969 bool "GZIP" 1970 1971config MODULE_COMPRESS_XZ 1972 bool "XZ" 1973 1974endchoice 1975 1976endif # MODULES 1977 1978config INIT_ALL_POSSIBLE 1979 bool 1980 help 1981 Back when each arch used to define their own cpu_online_mask and 1982 cpu_possible_mask, some of them chose to initialize cpu_possible_mask 1983 with all 1s, and others with all 0s. When they were centralised, 1984 it was better to provide this option than to break all the archs 1985 and have several arch maintainers pursuing me down dark alleys. 1986 1987config STOP_MACHINE 1988 bool 1989 default y 1990 depends on (SMP && MODULE_UNLOAD) || HOTPLUG_CPU 1991 help 1992 Need stop_machine() primitive. 1993 1994source "block/Kconfig" 1995 1996config PREEMPT_NOTIFIERS 1997 bool 1998 1999config PADATA 2000 depends on SMP 2001 bool 2002 2003# Can be selected by architectures with broken toolchains 2004# that get confused by correct const<->read_only section 2005# mappings 2006config BROKEN_RODATA 2007 bool 2008 2009config ASN1 2010 tristate 2011 help 2012 Build a simple ASN.1 grammar compiler that produces a bytecode output 2013 that can be interpreted by the ASN.1 stream decoder and used to 2014 inform it as to what tags are to be expected in a stream and what 2015 functions to call on what tags. 2016 2017source "kernel/Kconfig.locks" 2018