1. 17 8月, 2019 1 次提交
  2. 05 5月, 2018 1 次提交
  3. 04 3月, 2018 1 次提交
    • I
      sched/headers: Simplify and clean up header usage in the scheduler · 325ea10c
      Ingo Molnar 提交于
      Do the following cleanups and simplifications:
      
       - sched/sched.h already includes <asm/paravirt.h>, so no need to
         include it in sched/core.c again.
      
       - order the <linux/sched/*.h> headers alphabetically
      
       - add all <linux/sched/*.h> headers to kernel/sched/sched.h
      
       - remove all unnecessary includes from the .c files that
         are already included in kernel/sched/sched.h.
      
      Finally, make all scheduler .c files use a single common header:
      
        #include "sched.h"
      
      ... which now contains a union of the relied upon headers.
      
      This makes the various .c files easier to read and easier to handle.
      
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: linux-kernel@vger.kernel.org
      Signed-off-by: NIngo Molnar <mingo@kernel.org>
      325ea10c
  4. 03 3月, 2018 1 次提交
    • I
      sched: Clean up and harmonize the coding style of the scheduler code base · 97fb7a0a
      Ingo Molnar 提交于
      A good number of small style inconsistencies have accumulated
      in the scheduler core, so do a pass over them to harmonize
      all these details:
      
       - fix speling in comments,
      
       - use curly braces for multi-line statements,
      
       - remove unnecessary parentheses from integer literals,
      
       - capitalize consistently,
      
       - remove stray newlines,
      
       - add comments where necessary,
      
       - remove invalid/unnecessary comments,
      
       - align structure definitions and other data types vertically,
      
       - add missing newlines for increased readability,
      
       - fix vertical tabulation where it's misaligned,
      
       - harmonize preprocessor conditional block labeling
         and vertical alignment,
      
       - remove line-breaks where they uglify the code,
      
       - add newline after local variable definitions,
      
      No change in functionality:
      
        md5:
           1191fa0a890cfa8132156d2959d7e9e2  built-in.o.before.asm
           1191fa0a890cfa8132156d2959d7e9e2  built-in.o.after.asm
      
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: linux-kernel@vger.kernel.org
      Signed-off-by: NIngo Molnar <mingo@kernel.org>
      97fb7a0a
  5. 08 12月, 2017 2 次提交
  6. 02 11月, 2017 1 次提交
    • G
      License cleanup: add SPDX GPL-2.0 license identifier to files with no license · b2441318
      Greg Kroah-Hartman 提交于
      Many source files in the tree are missing licensing information, which
      makes it harder for compliance tools to determine the correct license.
      
      By default all files without license information are under the default
      license of the kernel, which is GPL version 2.
      
      Update the files which contain no license information with the 'GPL-2.0'
      SPDX license identifier.  The SPDX identifier is a legally binding
      shorthand, which can be used instead of the full boiler plate text.
      
      This patch is based on work done by Thomas Gleixner and Kate Stewart and
      Philippe Ombredanne.
      
      How this work was done:
      
      Patches were generated and checked against linux-4.14-rc6 for a subset of
      the use cases:
       - file had no licensing information it it.
       - file was a */uapi/* one with no licensing information in it,
       - file was a */uapi/* one with existing licensing information,
      
      Further patches will be generated in subsequent months to fix up cases
      where non-standard license headers were used, and references to license
      had to be inferred by heuristics based on keywords.
      
      The analysis to determine which SPDX License Identifier to be applied to
      a file was done in a spreadsheet of side by side results from of the
      output of two independent scanners (ScanCode & Windriver) producing SPDX
      tag:value files created by Philippe Ombredanne.  Philippe prepared the
      base worksheet, and did an initial spot review of a few 1000 files.
      
      The 4.13 kernel was the starting point of the analysis with 60,537 files
      assessed.  Kate Stewart did a file by file comparison of the scanner
      results in the spreadsheet to determine which SPDX license identifier(s)
      to be applied to the file. She confirmed any determination that was not
      immediately clear with lawyers working with the Linux Foundation.
      
      Criteria used to select files for SPDX license identifier tagging was:
       - Files considered eligible had to be source code files.
       - Make and config files were included as candidates if they contained >5
         lines of source
       - File already had some variant of a license header in it (even if <5
         lines).
      
      All documentation files were explicitly excluded.
      
      The following heuristics were used to determine which SPDX license
      identifiers to apply.
      
       - when both scanners couldn't find any license traces, file was
         considered to have no license information in it, and the top level
         COPYING file license applied.
      
         For non */uapi/* files that summary was:
      
         SPDX license identifier                            # files
         ---------------------------------------------------|-------
         GPL-2.0                                              11139
      
         and resulted in the first patch in this series.
      
         If that file was a */uapi/* path one, it was "GPL-2.0 WITH
         Linux-syscall-note" otherwise it was "GPL-2.0".  Results of that was:
      
         SPDX license identifier                            # files
         ---------------------------------------------------|-------
         GPL-2.0 WITH Linux-syscall-note                        930
      
         and resulted in the second patch in this series.
      
       - if a file had some form of licensing information in it, and was one
         of the */uapi/* ones, it was denoted with the Linux-syscall-note if
         any GPL family license was found in the file or had no licensing in
         it (per prior point).  Results summary:
      
         SPDX license identifier                            # files
         ---------------------------------------------------|------
         GPL-2.0 WITH Linux-syscall-note                       270
         GPL-2.0+ WITH Linux-syscall-note                      169
         ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause)    21
         ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)    17
         LGPL-2.1+ WITH Linux-syscall-note                      15
         GPL-1.0+ WITH Linux-syscall-note                       14
         ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause)    5
         LGPL-2.0+ WITH Linux-syscall-note                       4
         LGPL-2.1 WITH Linux-syscall-note                        3
         ((GPL-2.0 WITH Linux-syscall-note) OR MIT)              3
         ((GPL-2.0 WITH Linux-syscall-note) AND MIT)             1
      
         and that resulted in the third patch in this series.
      
       - when the two scanners agreed on the detected license(s), that became
         the concluded license(s).
      
       - when there was disagreement between the two scanners (one detected a
         license but the other didn't, or they both detected different
         licenses) a manual inspection of the file occurred.
      
       - In most cases a manual inspection of the information in the file
         resulted in a clear resolution of the license that should apply (and
         which scanner probably needed to revisit its heuristics).
      
       - When it was not immediately clear, the license identifier was
         confirmed with lawyers working with the Linux Foundation.
      
       - If there was any question as to the appropriate license identifier,
         the file was flagged for further research and to be revisited later
         in time.
      
      In total, over 70 hours of logged manual review was done on the
      spreadsheet to determine the SPDX license identifiers to apply to the
      source files by Kate, Philippe, Thomas and, in some cases, confirmation
      by lawyers working with the Linux Foundation.
      
      Kate also obtained a third independent scan of the 4.13 code base from
      FOSSology, and compared selected files where the other two scanners
      disagreed against that SPDX file, to see if there was new insights.  The
      Windriver scanner is based on an older version of FOSSology in part, so
      they are related.
      
      Thomas did random spot checks in about 500 files from the spreadsheets
      for the uapi headers and agreed with SPDX license identifier in the
      files he inspected. For the non-uapi files Thomas did random spot checks
      in about 15000 files.
      
      In initial set of patches against 4.14-rc6, 3 files were found to have
      copy/paste license identifier errors, and have been fixed to reflect the
      correct identifier.
      
      Additionally Philippe spent 10 hours this week doing a detailed manual
      inspection and review of the 12,461 patched files from the initial patch
      version early this week with:
       - a full scancode scan run, collecting the matched texts, detected
         license ids and scores
       - reviewing anything where there was a license detected (about 500+
         files) to ensure that the applied SPDX license was correct
       - reviewing anything where there was no detection but the patch license
         was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
         SPDX license was correct
      
      This produced a worksheet with 20 files needing minor correction.  This
      worksheet was then exported into 3 different .csv files for the
      different types of files to be modified.
      
      These .csv files were then reviewed by Greg.  Thomas wrote a script to
      parse the csv files and add the proper SPDX tag to the file, in the
      format that the file expected.  This script was further refined by Greg
      based on the output to detect more types of files automatically and to
      distinguish between header and source .c files (which need different
      comment types.)  Finally Greg ran the script using the .csv files to
      generate the patches.
      Reviewed-by: NKate Stewart <kstewart@linuxfoundation.org>
      Reviewed-by: NPhilippe Ombredanne <pombredanne@nexb.com>
      Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
      Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      b2441318
  7. 10 8月, 2017 1 次提交
  8. 08 2月, 2017 1 次提交
    • I
      sched/autogroup: Rename auto_group.[ch] to autogroup.[ch] · 1051408f
      Ingo Molnar 提交于
      The names are all 'autogroup', not 'auto_group' - so rename
      the kernel/sched/auto_group.[ch] to match the existing
      nomenclature.
      
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: linux-kernel@vger.kernel.org
      Signed-off-by: NIngo Molnar <mingo@kernel.org>
      1051408f
  9. 24 11月, 2016 1 次提交
    • M
      sched/autogroup: Fix 64-bit kernel nice level adjustment · 83929cce
      Mike Galbraith 提交于
      Michael Kerrisk reported:
      
      > Regarding the previous paragraph...  My tests indicate
      > that writing *any* value to the autogroup [nice priority level]
      > file causes the task group to get a lower priority.
      
      Because autogroup didn't call the then meaningless scale_load()...
      
      Autogroup nice level adjustment has been broken ever since load
      resolution was increased for 64-bit kernels.  Use scale_load() to
      scale group weight.
      
      Michael Kerrisk tested this patch to fix the problem:
      
      > Applied and tested against 4.9-rc6 on an Intel u7 (4 cores).
      > Test setup:
      >
      > Terminal window 1: running 40 CPU burner jobs
      > Terminal window 2: running 40 CPU burner jobs
      > Terminal window 1: running  1 CPU burner job
      >
      > Demonstrated that:
      > * Writing "0" to the autogroup file for TW1 now causes no change
      >   to the rate at which the process on the terminal consume CPU.
      > * Writing -20 to the autogroup file for TW1 caused those processes
      >   to get the lion's share of CPU while TW2 TW3 get a tiny amount.
      > * Writing -20 to the autogroup files for TW1 and TW3 allowed the
      >   process on TW3 to get as much CPU as it was getting as when
      >   the autogroup nice values for both terminals were 0.
      Reported-by: NMichael Kerrisk <mtk.manpages@gmail.com>
      Tested-by: NMichael Kerrisk <mtk.manpages@gmail.com>
      Signed-off-by: NMike Galbraith <umgwanakikbuti@gmail.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: linux-man <linux-man@vger.kernel.org>
      Cc: stable@vger.kernel.org
      Link: http://lkml.kernel.org/r/1479897217.4306.6.camel@gmx.deSigned-off-by: NIngo Molnar <mingo@kernel.org>
      83929cce
  10. 22 11月, 2016 2 次提交
    • O
      sched/autogroup: Do not use autogroup->tg in zombie threads · 8e5bfa8c
      Oleg Nesterov 提交于
      Exactly because for_each_thread() in autogroup_move_group() can't see it
      and update its ->sched_task_group before _put() and possibly free().
      
      So the exiting task needs another sched_move_task() before exit_notify()
      and we need to re-introduce the PF_EXITING (or similar) check removed by
      the previous change for another reason.
      Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: hartsjc@redhat.com
      Cc: vbendel@redhat.com
      Cc: vlovejoy@redhat.com
      Link: http://lkml.kernel.org/r/20161114184612.GA15968@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      8e5bfa8c
    • O
      sched/autogroup: Fix autogroup_move_group() to never skip sched_move_task() · 18f649ef
      Oleg Nesterov 提交于
      The PF_EXITING check in task_wants_autogroup() is no longer needed. Remove
      it, but see the next patch.
      
      However the comment is correct in that autogroup_move_group() must always
      change task_group() for every thread so the sysctl_ check is very wrong;
      we can race with cgroups and even sys_setsid() is not safe because a task
      running with task_group() == ag->tg must participate in refcounting:
      
      	int main(void)
      	{
      		int sctl = open("/proc/sys/kernel/sched_autogroup_enabled", O_WRONLY);
      
      		assert(sctl > 0);
      		if (fork()) {
      			wait(NULL); // destroy the child's ag/tg
      			pause();
      		}
      
      		assert(pwrite(sctl, "1\n", 2, 0) == 2);
      		assert(setsid() > 0);
      		if (fork())
      			pause();
      
      		kill(getppid(), SIGKILL);
      		sleep(1);
      
      		// The child has gone, the grandchild runs with kref == 1
      		assert(pwrite(sctl, "0\n", 2, 0) == 2);
      		assert(setsid() > 0);
      
      		// runs with the freed ag/tg
      		for (;;)
      			sleep(1);
      
      		return 0;
      	}
      
      crashes the kernel. It doesn't really need sleep(1), it doesn't matter if
      autogroup_move_group() actually frees the task_group or this happens later.
      Reported-by: NVern Lovejoy <vlovejoy@redhat.com>
      Signed-off-by: NOleg Nesterov <oleg@redhat.com>
      Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: hartsjc@redhat.com
      Cc: vbendel@redhat.com
      Link: http://lkml.kernel.org/r/20161114184609.GA15965@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
      18f649ef
  11. 04 12月, 2015 1 次提交
  12. 08 5月, 2015 1 次提交
  13. 16 4月, 2015 1 次提交
  14. 18 2月, 2015 1 次提交
    • P
      sched/autogroup: Fix failure to set cpu.rt_runtime_us · 1fe89e1b
      Peter Zijlstra 提交于
      Because task_group() uses a cache of autogroup_task_group(), whose
      output depends on sched_class, switching classes can generate
      problems.
      
      In particular, when started as fair, the cache points to the
      autogroup, so when switching to RT the tg_rt_schedulable() test fails
      for every cpu.rt_{runtime,period}_us change because now the autogroup
      has tasks and no runtime.
      
      Furthermore, going back to the previous semantics of varying
      task_group() with sched_class has the down-side that the sched_debug
      output varies as well, even though the task really is in the
      autogroup.
      
      Therefore add an autogroup exception to tg_has_rt_tasks() -- such that
      both (all) task_group() usages in sched/core now have one. And remove
      all the remnants of the variable task_group() output.
      Reported-by: NZefan Li <lizefan@huawei.com>
      Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
      Cc: Stefan Bader <stefan.bader@canonical.com>
      Fixes: 8323f26c ("sched: Fix race in task_group()")
      Link: http://lkml.kernel.org/r/20150209112237.GR5029@twins.programming.kicks-ass.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      1fe89e1b
  15. 20 8月, 2014 1 次提交
  16. 23 2月, 2014 1 次提交
  17. 28 5月, 2013 1 次提交
  18. 25 1月, 2013 1 次提交
    • L
      sched: split out css_online/css_offline from tg creation/destruction · ace783b9
      Li Zefan 提交于
      This is a preparaton for later patches.
      
      - What do we gain from cpu_cgroup_css_online():
      
      After ss->css_alloc() and before ss->css_online(), there's a small
      window that tg->css.cgroup is NULL. With this change, tg won't be seen
      before ss->css_online(), where it's added to the global list, so we're
      guaranteed we'll never see NULL tg->css.cgroup.
      
      - What do we gain from cpu_cgroup_css_offline():
      
      tg is freed via RCU, so is cgroup. Without this change, This is how
      synchronization works:
      
      cgroup_rmdir()
        no ss->css_offline()
      diput()
        syncornize_rcu()
        ss->css_free()       <-- unregister tg, and free it via call_rcu()
        kfree_rcu(cgroup)    <-- wait possible refs to cgroup, and free cgroup
      
      We can't just kfree(cgroup), because tg might access tg->css.cgroup.
      
      With this change:
      
      cgroup_rmdir()
        ss->css_offline()    <-- unregister tg
      diput()
        synchronize_rcu()    <-- wait possible refs to tg and cgroup
        ss->css_free()       <-- free tg
        kfree_rcu(cgroup)    <-- free cgroup
      
      As you see, kfree_rcu() is redundant now.
      Signed-off-by: NLi Zefan <lizefan@huawei.com>
      Signed-off-by: NTejun Heo <tj@kernel.org>
      Acked-by: NIngo Molnar <mingo@kernel.org>
      ace783b9
  19. 11 12月, 2012 1 次提交
  20. 04 12月, 2012 1 次提交
    • M
      Revert "sched, autogroup: Stop going ahead if autogroup is disabled" · fd8ef117
      Mike Galbraith 提交于
      This reverts commit 800d4d30.
      
      Between commits 8323f26c ("sched: Fix race in task_group()") and
      800d4d30 ("sched, autogroup: Stop going ahead if autogroup is
      disabled"), autogroup is a wreck.
      
      With both applied, all you have to do to crash a box is disable
      autogroup during boot up, then reboot..  boom, NULL pointer dereference
      due to commit 800d4d30 not allowing autogroup to move things, and
      commit 8323f26c making that the only way to switch runqueues:
      
        BUG: unable to handle kernel NULL pointer dereference at           (null)
        IP: [<ffffffff81063ac0>] effective_load.isra.43+0x50/0x90
        Pid: 7047, comm: systemd-user-se Not tainted 3.6.8-smp #7 MEDIONPC MS-7502/MS-7502
        RIP: effective_load.isra.43+0x50/0x90
        Process systemd-user-se (pid: 7047, threadinfo ffff880221dde000, task ffff88022618b3a0)
        Call Trace:
          select_task_rq_fair+0x255/0x780
          try_to_wake_up+0x156/0x2c0
          wake_up_state+0xb/0x10
          signal_wake_up+0x28/0x40
          complete_signal+0x1d6/0x250
          __send_signal+0x170/0x310
          send_signal+0x40/0x80
          do_send_sig_info+0x47/0x90
          group_send_sig_info+0x4a/0x70
          kill_pid_info+0x3a/0x60
          sys_kill+0x97/0x1a0
          ? vfs_read+0x120/0x160
          ? sys_read+0x45/0x90
          system_call_fastpath+0x16/0x1b
        Code: 49 0f af 41 50 31 d2 49 f7 f0 48 83 f8 01 48 0f 46 c6 48 2b 07 48 8b bf 40 01 00 00 48 85 ff 74 3a 45 31 c0 48 8b 8f 50 01 00 00 <48> 8b 11 4c 8b 89 80 00 00 00 49 89 d2 48 01 d0 45 8b 59 58 4c
        RIP  [<ffffffff81063ac0>] effective_load.isra.43+0x50/0x90
         RSP <ffff880221ddfbd8>
        CR2: 0000000000000000
      Signed-off-by: NMike Galbraith <efault@gmx.de>
      Acked-by: NIngo Molnar <mingo@kernel.org>
      Cc: Yong Zhang <yong.zhang0@gmail.com>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: stable@vger.kernel.org # 2.6.39+
      Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      fd8ef117
  21. 30 10月, 2012 1 次提交
    • M
      sched/autogroup: Fix crash on reboot when autogroup is disabled · 5258f386
      Mike Galbraith 提交于
      Due to these two commits:
      
        8323f26c sched: Fix race in task_group()
        800d4d30 sched, autogroup: Stop going ahead if autogroup is disabled
      
      ... autogroup scheduling's dynamic knobs are wrecked.
      
      With both patches applied, all you have to do to crash a box is
      disable autogroup during boot up, then reboot.. boom, NULL pointer
      dereference due to 800d4d30 not allowing autogroup to move things,
      and 8323f26c making that the only way to switch runqueues.
      
      Remove most of the (dysfunctional) knobs and turn the remaining
      sched_autogroup_enabled knob readonly.
      
      If the user fiddles with cgroups hereafter, once tasks
      are moved, autogroup won't mess with them again unless
      they call setsid().
      
      No knobs, no glitz, nada, just a cute little thing folks can
      turn on if they don't want to muck about with cgroups and/or
      systemd.
      Signed-off-by: NMike Galbraith <efault@gmx.de>
      Cc: Xiaotian Feng <xtfeng@gmail.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Xiaotian Feng <dannyfeng@tencent.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: <stable@vger.kernel.org> # v3.6
      Link: http://lkml.kernel.org/r/1351451963.4999.8.camel@maggy.simpson.netSigned-off-by: NIngo Molnar <mingo@kernel.org>
      5258f386
  22. 02 3月, 2012 1 次提交
  23. 17 11月, 2011 2 次提交
  24. 31 3月, 2011 1 次提交
  25. 23 2月, 2011 2 次提交
  26. 18 1月, 2011 2 次提交
  27. 07 1月, 2011 2 次提交
  28. 04 1月, 2011 1 次提交
  29. 30 11月, 2010 1 次提交
    • M
      sched: Add 'autogroup' scheduling feature: automated per session task groups · 5091faa4
      Mike Galbraith 提交于
      A recurring complaint from CFS users is that parallel kbuild has
      a negative impact on desktop interactivity.  This patch
      implements an idea from Linus, to automatically create task
      groups.  Currently, only per session autogroups are implemented,
      but the patch leaves the way open for enhancement.
      
      Implementation: each task's signal struct contains an inherited
      pointer to a refcounted autogroup struct containing a task group
      pointer, the default for all tasks pointing to the
      init_task_group.  When a task calls setsid(), a new task group
      is created, the process is moved into the new task group, and a
      reference to the preveious task group is dropped.  Child
      processes inherit this task group thereafter, and increase it's
      refcount.  When the last thread of a process exits, the
      process's reference is dropped, such that when the last process
      referencing an autogroup exits, the autogroup is destroyed.
      
      At runqueue selection time, IFF a task has no cgroup assignment,
      its current autogroup is used.
      
      Autogroup bandwidth is controllable via setting it's nice level
      through the proc filesystem:
      
        cat /proc/<pid>/autogroup
      
      Displays the task's group and the group's nice level.
      
        echo <nice level> > /proc/<pid>/autogroup
      
      Sets the task group's shares to the weight of nice <level> task.
      Setting nice level is rate limited for !admin users due to the
      abuse risk of task group locking.
      
      The feature is enabled from boot by default if
      CONFIG_SCHED_AUTOGROUP=y is selected, but can be disabled via
      the boot option noautogroup, and can also be turned on/off on
      the fly via:
      
        echo [01] > /proc/sys/kernel/sched_autogroup_enabled
      
      ... which will automatically move tasks to/from the root task group.
      Signed-off-by: NMike Galbraith <efault@gmx.de>
      Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
      Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Markus Trippelsdorf <markus@trippelsdorf.de>
      Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
      Cc: Paul Turner <pjt@google.com>
      Cc: Oleg Nesterov <oleg@redhat.com>
      [ Removed the task_group_path() debug code, and fixed !EVENTFD build failure. ]
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      LKML-Reference: <1290281700.28711.9.camel@maggy.simson.net>
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      5091faa4