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  1. 24 3月, 2012 1 次提交
    • L
      prctl: add PR_{SET,GET}_CHILD_SUBREAPER to allow simple process supervision · ebec18a6
      由 Lennart Poettering 提交于 
      Userspace service managers/supervisors need to track their started
services.  Many services daemonize by double-forking and get implicitly
re-parented to PID 1.  The service manager will no longer be able to
receive the SIGCHLD signals for them, and is no longer in charge of
reaping the children with wait().  All information about the children is
lost at the moment PID 1 cleans up the re-parented processes.

With this prctl, a service manager process can mark itself as a sort of
'sub-init', able to stay as the parent for all orphaned processes
created by the started services.  All SIGCHLD signals will be delivered
to the service manager.

Receiving SIGCHLD and doing wait() is in cases of a service-manager much
preferred over any possible asynchronous notification about specific
PIDs, because the service manager has full access to the child process
data in /proc and the PID can not be re-used until the wait(), the
service-manager itself is in charge of, has happened.

As a side effect, the relevant parent PID information does not get lost
by a double-fork, which results in a more elaborate process tree and
'ps' output:

before:
  # ps afx
  253 ?        Ss     0:00 /bin/dbus-daemon --system --nofork
  294 ?        Sl     0:00 /usr/libexec/polkit-1/polkitd
  328 ?        S      0:00 /usr/sbin/modem-manager
  608 ?        Sl     0:00 /usr/libexec/colord
  658 ?        Sl     0:00 /usr/libexec/upowerd
  819 ?        Sl     0:00 /usr/libexec/imsettings-daemon
  916 ?        Sl     0:00 /usr/libexec/udisks-daemon
  917 ?        S      0:00  \_ udisks-daemon: not polling any devices

after:
  # ps afx
  294 ?        Ss     0:00 /bin/dbus-daemon --system --nofork
  426 ?        Sl     0:00  \_ /usr/libexec/polkit-1/polkitd
  449 ?        S      0:00  \_ /usr/sbin/modem-manager
  635 ?        Sl     0:00  \_ /usr/libexec/colord
  705 ?        Sl     0:00  \_ /usr/libexec/upowerd
  959 ?        Sl     0:00  \_ /usr/libexec/udisks-daemon
  960 ?        S      0:00  |   \_ udisks-daemon: not polling any devices
  977 ?        Sl     0:00  \_ /usr/libexec/packagekitd

This prctl is orthogonal to PID namespaces.  PID namespaces are isolated
from each other, while a service management process usually requires the
services to live in the same namespace, to be able to talk to each
other.

Users of this will be the systemd per-user instance, which provides
init-like functionality for the user's login session and D-Bus, which
activates bus services on-demand.  Both need init-like capabilities to
be able to properly keep track of the services they start.

Many thanks to Oleg for several rounds of review and insights.

[akpm@linux-foundation.org: fix comment layout and spelling]
[akpm@linux-foundation.org: add lengthy code comment from Oleg]
Reviewed-by: NOleg Nesterov <oleg@redhat.com>
Signed-off-by: NLennart Poettering <lennart@poettering.net>
Signed-off-by: NKay Sievers <kay.sievers@vrfy.org>
Acked-by: NValdis Kletnieks <Valdis.Kletnieks@vt.edu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      ebec18a6
  3. 22 3月, 2012 1 次提交
    • M
      cpuset: mm: reduce large amounts of memory barrier related damage v3 · cc9a6c87
      由 Mel Gorman 提交于 
      Commit c0ff7453 ("cpuset,mm: fix no node to alloc memory when
changing cpuset's mems") wins a super prize for the largest number of
memory barriers entered into fast paths for one commit.

[get|put]_mems_allowed is incredibly heavy with pairs of full memory
barriers inserted into a number of hot paths.  This was detected while
investigating at large page allocator slowdown introduced some time
after 2.6.32.  The largest portion of this overhead was shown by
oprofile to be at an mfence introduced by this commit into the page
allocator hot path.

For extra style points, the commit introduced the use of yield() in an
implementation of what looks like a spinning mutex.

This patch replaces the full memory barriers on both read and write
sides with a sequence counter with just read barriers on the fast path
side.  This is much cheaper on some architectures, including x86.  The
main bulk of the patch is the retry logic if the nodemask changes in a
manner that can cause a false failure.

While updating the nodemask, a check is made to see if a false failure
is a risk.  If it is, the sequence number gets bumped and parallel
allocators will briefly stall while the nodemask update takes place.

In a page fault test microbenchmark, oprofile samples from
__alloc_pages_nodemask went from 4.53% of all samples to 1.15%.  The
actual results were

                             3.3.0-rc3          3.3.0-rc3
                             rc3-vanilla        nobarrier-v2r1
    Clients   1 UserTime       0.07 (  0.00%)   0.08 (-14.19%)
    Clients   2 UserTime       0.07 (  0.00%)   0.07 (  2.72%)
    Clients   4 UserTime       0.08 (  0.00%)   0.07 (  3.29%)
    Clients   1 SysTime        0.70 (  0.00%)   0.65 (  6.65%)
    Clients   2 SysTime        0.85 (  0.00%)   0.82 (  3.65%)
    Clients   4 SysTime        1.41 (  0.00%)   1.41 (  0.32%)
    Clients   1 WallTime       0.77 (  0.00%)   0.74 (  4.19%)
    Clients   2 WallTime       0.47 (  0.00%)   0.45 (  3.73%)
    Clients   4 WallTime       0.38 (  0.00%)   0.37 (  1.58%)
    Clients   1 Flt/sec/cpu  497620.28 (  0.00%) 520294.53 (  4.56%)
    Clients   2 Flt/sec/cpu  414639.05 (  0.00%) 429882.01 (  3.68%)
    Clients   4 Flt/sec/cpu  257959.16 (  0.00%) 258761.48 (  0.31%)
    Clients   1 Flt/sec      495161.39 (  0.00%) 517292.87 (  4.47%)
    Clients   2 Flt/sec      820325.95 (  0.00%) 850289.77 (  3.65%)
    Clients   4 Flt/sec      1020068.93 (  0.00%) 1022674.06 (  0.26%)
    MMTests Statistics: duration
    Sys Time Running Test (seconds)             135.68    132.17
    User+Sys Time Running Test (seconds)         164.2    160.13
    Total Elapsed Time (seconds)                123.46    120.87

The overall improvement is small but the System CPU time is much
improved and roughly in correlation to what oprofile reported (these
performance figures are without profiling so skew is expected).  The
actual number of page faults is noticeably improved.

For benchmarks like kernel builds, the overall benefit is marginal but
the system CPU time is slightly reduced.

To test the actual bug the commit fixed I opened two terminals.  The
first ran within a cpuset and continually ran a small program that
faulted 100M of anonymous data.  In a second window, the nodemask of the
cpuset was continually randomised in a loop.

Without the commit, the program would fail every so often (usually
within 10 seconds) and obviously with the commit everything worked fine.
With this patch applied, it also worked fine so the fix should be
functionally equivalent.
Signed-off-by: NMel Gorman <mgorman@suse.de>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      cc9a6c87
  5. 10 3月, 2012 1 次提交
  7. 06 3月, 2012 4 次提交
  9. 02 3月, 2012 1 次提交
  11. 01 3月, 2012 2 次提交
  13. 22 2月, 2012 2 次提交
  15. 11 2月, 2012 1 次提交
  17. 03 2月, 2012 1 次提交
  19. 27 1月, 2012 2 次提交
  21. 24 1月, 2012 1 次提交
    • R
      kernel-doc: fix kernel-doc warnings in sched · fa757281
      由 Randy Dunlap 提交于 
      Fix new kernel-doc notation warnings:

Warning(include/linux/sched.h:2094): No description found for parameter 'p'
Warning(include/linux/sched.h:2094): Excess function parameter 'tsk' description in 'is_idle_task'
Warning(kernel/sched/cpupri.c:139): No description found for parameter 'newpri'
Warning(kernel/sched/cpupri.c:139): Excess function parameter 'pri' description in 'cpupri_set'
Warning(kernel/sched/cpupri.c:208): Excess function parameter 'bootmem' description in 'cpupri_init'
Signed-off-by: NRandy Dunlap <rdunlap@xenotime.net>
Cc:	Ingo Molnar <mingo@elte.hu>
Cc:	Peter Zijlstra <peterz@infradead.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      fa757281
  23. 17 1月, 2012 1 次提交
  25. 13 1月, 2012 1 次提交
  27. 18 12月, 2011 1 次提交
    • W
      writeback: dirty ratelimit - think time compensation · 83712358
      由 Wu Fengguang 提交于 
      Compensate the task's think time when computing the final pause time,
so that ->dirty_ratelimit can be executed accurately.

        think time := time spend outside of balance_dirty_pages()

In the rare case that the task slept longer than the 200ms period time
(result in negative pause time), the sleep time will be compensated in
the following periods, too, if it's less than 1 second.

Accumulated errors are carefully avoided as long as the max pause area
is not hitted.

Pseudo code:

        period = pages_dirtied / task_ratelimit;
        think = jiffies - dirty_paused_when;
        pause = period - think;

1) normal case: period > think

        pause = period - think
        dirty_paused_when = jiffies + pause
        nr_dirtied = 0

                             period time
              |===============================>|
                  think time      pause time
              |===============>|==============>|
        ------|----------------|---------------|------------------------
        dirty_paused_when   jiffies

2) no pause case: period <= think

        don't pause; reduce future pause time by:
        dirty_paused_when += period
        nr_dirtied = 0

                           period time
              |===============================>|
                                  think time
              |===================================================>|
        ------|--------------------------------+-------------------|----
        dirty_paused_when                                       jiffies
Acked-by: NJan Kara <jack@suse.cz>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>
      83712358
  29. 15 12月, 2011 2 次提交
  31. 13 12月, 2011 2 次提交
    • T
      threadgroup: extend threadgroup_lock() to cover exit and exec · 77e4ef99
      由 Tejun Heo 提交于 
      threadgroup_lock() protected only protected against new addition to
the threadgroup, which was inherently somewhat incomplete and
problematic for its only user cgroup.  On-going migration could race
against exec and exit leading to interesting problems - the symmetry
between various attach methods, task exiting during method execution,
->exit() racing against attach methods, migrating task switching basic
properties during exec and so on.

This patch extends threadgroup_lock() such that it protects against
all three threadgroup altering operations - fork, exit and exec.  For
exit, threadgroup_change_begin/end() calls are added to exit_signals
around assertion of PF_EXITING.  For exec, threadgroup_[un]lock() are
updated to also grab and release cred_guard_mutex.

With this change, threadgroup_lock() guarantees that the target
threadgroup will remain stable - no new task will be added, no new
PF_EXITING will be set and exec won't happen.

The next patch will update cgroup so that it can take full advantage
of this change.

-v2: beefed up comment as suggested by Frederic.

-v3: narrowed scope of protection in exit path as suggested by
     Frederic.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: NLi Zefan <lizf@cn.fujitsu.com>
Acked-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
      77e4ef99
    • T
      threadgroup: rename signal->threadgroup_fork_lock to ->group_rwsem · 257058ae
      由 Tejun Heo 提交于 
      Make the following renames to prepare for extension of threadgroup
locking.

* s/signal->threadgroup_fork_lock/signal->group_rwsem/
* s/threadgroup_fork_read_lock()/threadgroup_change_begin()/
* s/threadgroup_fork_read_unlock()/threadgroup_change_end()/
* s/threadgroup_fork_write_lock()/threadgroup_lock()/
* s/threadgroup_fork_write_unlock()/threadgroup_unlock()/

This patch doesn't cause any behavior change.

-v2: Rename threadgroup_change_done() to threadgroup_change_end() per
     KAMEZAWA's suggestion.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: NLi Zefan <lizf@cn.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <paul@paulmenage.org>
      257058ae
  33. 12 12月, 2011 1 次提交
  35. 07 12月, 2011 1 次提交
  37. 06 12月, 2011 1 次提交
  39. 24 11月, 2011 1 次提交
    • T
      freezer: kill unused set_freezable_with_signal() · 34b087e4
      由 Tejun Heo 提交于 
      There's no in-kernel user of set_freezable_with_signal() left.  Mixing
TIF_SIGPENDING with kernel threads can lead to nasty corner cases as
kernel threads never travel signal delivery path on their own.

e.g. the current implementation is buggy in the cancelation path of
__thaw_task().  It calls recalc_sigpending_and_wake() in an attempt to
clear TIF_SIGPENDING but the function never clears it regardless of
sigpending state.  This means that signallable freezable kthreads may
continue executing with !freezing() && stuck TIF_SIGPENDING, which can
be troublesome.

This patch removes set_freezable_with_signal() along with
PF_FREEZER_NOSIG and recalc_sigpending*() calls in freezer.  User
tasks get TIF_SIGPENDING, kernel tasks get woken up and the spurious
sigpending is dealt with in the usual signal delivery path.
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NOleg Nesterov <oleg@redhat.com>
      34b087e4
  41. 22 11月, 2011 1 次提交
    • T
      freezer: kill PF_FREEZING · 376fede8
      由 Tejun Heo 提交于 
      With the previous changes, there's no meaningful difference between
PF_FREEZING and PF_FROZEN.  Remove PF_FREEZING and use PF_FROZEN
instead in task_contributes_to_load().
Signed-off-by: NTejun Heo <tj@kernel.org>
      376fede8
  43. 17 11月, 2011 2 次提交
  45. 04 10月, 2011 1 次提交
  47. 03 10月, 2011 1 次提交
    • W
      writeback: per task dirty rate limit · 9d823e8f
      由 Wu Fengguang 提交于 
      Add two fields to task_struct.

1) account dirtied pages in the individual tasks, for accuracy
2) per-task balance_dirty_pages() call intervals, for flexibility

The balance_dirty_pages() call interval (ie. nr_dirtied_pause) will
scale near-sqrt to the safety gap between dirty pages and threshold.

The main problem of per-task nr_dirtied is, if 1k+ tasks start dirtying
pages at exactly the same time, each task will be assigned a large
initial nr_dirtied_pause, so that the dirty threshold will be exceeded
long before each task reached its nr_dirtied_pause and hence call
balance_dirty_pages().

The solution is to watch for the number of pages dirtied on each CPU in
between the calls into balance_dirty_pages(). If it exceeds ratelimit_pages
(3% dirty threshold), force call balance_dirty_pages() for a chance to
set bdi->dirty_exceeded. In normal situations, this safeguarding
condition is not expected to trigger at all.

On the sqrt in dirty_poll_interval():

It will serve as an initial guess when dirty pages are still in the
freerun area.

When dirty pages are floating inside the dirty control scope [freerun,
limit], a followup patch will use some refined dirty poll interval to
get the desired pause time.

   thresh-dirty (MB)    sqrt
		   1      16
		   2      22
		   4      32
		   8      45
		  16      64
		  32      90
		  64     128
		 128     181
		 256     256
		 512     362
		1024     512

The above table means, given 1MB (or 1GB) gap and the dd tasks polling
balance_dirty_pages() on every 16 (or 512) pages, the dirty limit won't
be exceeded as long as there are less than 16 (or 512) concurrent dd's.

So sqrt naturally leads to less overheads and more safe concurrent tasks
for large memory servers, which have large (thresh-freerun) gaps.

peter: keep the per-CPU ratelimit for safeguarding the 1k+ tasks case

CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: NAndrea Righi <andrea@betterlinux.com>
Signed-off-by: NWu Fengguang <fengguang.wu@intel.com>
      9d823e8f
  49. 30 9月, 2011 2 次提交
    • P
      posix-cpu-timers: Cure SMP wobbles · d670ec13
      由 Peter Zijlstra 提交于 
      David reported:

  Attached below is a watered-down version of rt/tst-cpuclock2.c from
  GLIBC.  Just build it with "gcc -o test test.c -lpthread -lrt" or
  similar.

  Run it several times, and you will see cases where the main thread
  will measure a process clock difference before and after the nanosleep
  which is smaller than the cpu-burner thread's individual thread clock
  difference.  This doesn't make any sense since the cpu-burner thread
  is part of the top-level process's thread group.

  I've reproduced this on both x86-64 and sparc64 (using both 32-bit and
  64-bit binaries).

  For example:

  [davem@boricha build-x86_64-linux]$ ./test
  process: before(0.001221967) after(0.498624371) diff(497402404)
  thread:  before(0.000081692) after(0.498316431) diff(498234739)
  self:    before(0.001223521) after(0.001240219) diff(16698)
  [davem@boricha build-x86_64-linux]$ 

  The diff of 'process' should always be >= the diff of 'thread'.

  I make sure to wrap the 'thread' clock measurements the most tightly
  around the nanosleep() call, and that the 'process' clock measurements
  are the outer-most ones.

  ---
  #include <unistd.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <time.h>
  #include <fcntl.h>
  #include <string.h>
  #include <errno.h>
  #include <pthread.h>

  static pthread_barrier_t barrier;

  static void *chew_cpu(void *arg)
  {
	  pthread_barrier_wait(&barrier);
	  while (1)
		  __asm__ __volatile__("" : : : "memory");
	  return NULL;
  }

  int main(void)
  {
	  clockid_t process_clock, my_thread_clock, th_clock;
	  struct timespec process_before, process_after;
	  struct timespec me_before, me_after;
	  struct timespec th_before, th_after;
	  struct timespec sleeptime;
	  unsigned long diff;
	  pthread_t th;
	  int err;

	  err = clock_getcpuclockid(0, &process_clock);
	  if (err)
		  return 1;

	  err = pthread_getcpuclockid(pthread_self(), &my_thread_clock);
	  if (err)
		  return 1;

	  pthread_barrier_init(&barrier, NULL, 2);
	  err = pthread_create(&th, NULL, chew_cpu, NULL);
	  if (err)
		  return 1;

	  err = pthread_getcpuclockid(th, &th_clock);
	  if (err)
		  return 1;

	  pthread_barrier_wait(&barrier);

	  err = clock_gettime(process_clock, &process_before);
	  if (err)
		  return 1;

	  err = clock_gettime(my_thread_clock, &me_before);
	  if (err)
		  return 1;

	  err = clock_gettime(th_clock, &th_before);
	  if (err)
		  return 1;

	  sleeptime.tv_sec = 0;
	  sleeptime.tv_nsec = 500000000;
	  nanosleep(&sleeptime, NULL);

	  err = clock_gettime(th_clock, &th_after);
	  if (err)
		  return 1;

	  err = clock_gettime(my_thread_clock, &me_after);
	  if (err)
		  return 1;

	  err = clock_gettime(process_clock, &process_after);
	  if (err)
		  return 1;

	  diff = process_after.tv_nsec - process_before.tv_nsec;
	  printf("process: before(%lu.%.9lu) after(%lu.%.9lu) diff(%lu)\n",
		 process_before.tv_sec, process_before.tv_nsec,
		 process_after.tv_sec, process_after.tv_nsec, diff);
	  diff = th_after.tv_nsec - th_before.tv_nsec;
	  printf("thread:  before(%lu.%.9lu) after(%lu.%.9lu) diff(%lu)\n",
		 th_before.tv_sec, th_before.tv_nsec,
		 th_after.tv_sec, th_after.tv_nsec, diff);
	  diff = me_after.tv_nsec - me_before.tv_nsec;
	  printf("self:    before(%lu.%.9lu) after(%lu.%.9lu) diff(%lu)\n",
		 me_before.tv_sec, me_before.tv_nsec,
		 me_after.tv_sec, me_after.tv_nsec, diff);

	  return 0;
  }

This is due to us using p->se.sum_exec_runtime in
thread_group_cputime() where we iterate the thread group and sum all
data. This does not take time since the last schedule operation (tick
or otherwise) into account. We can cure this by using
task_sched_runtime() at the cost of having to take locks.

This also means we can (and must) do away with
thread_group_sched_runtime() since the modified thread_group_cputime()
is now more accurate and would deadlock when called from
thread_group_sched_runtime().

Aside of that it makes the function safe on 32 bit systems. The old
code added t->se.sum_exec_runtime unprotected. sum_exec_runtime is a
64bit value and could be changed on another cpu at the same time.
Reported-by: NDavid Miller <davem@davemloft.net>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org
Link: http://lkml.kernel.org/r/1314874459.7945.22.camel@twinsTested-by: NDavid Miller <davem@davemloft.net>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      d670ec13
    • S
      user namespace: usb: make usb urbs user namespace aware (v2) · d178bc3a
      由 Serge Hallyn 提交于 
      Add to the dev_state and alloc_async structures the user namespace
corresponding to the uid and euid.  Pass these to kill_pid_info_as_uid(),
which can then implement a proper, user-namespace-aware uid check.

Changelog:
Sep 20: Per Oleg's suggestion: Instead of caching and passing user namespace,
	uid, and euid each separately, pass a struct cred.
Sep 26: Address Alan Stern's comments: don't define a struct cred at
	usbdev_open(), and take and put a cred at async_completed() to
	ensure it lasts for the duration of kill_pid_info_as_cred().
Signed-off-by: NSerge Hallyn <serge.hallyn@canonical.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>
      d178bc3a
  51. 29 9月, 2011 2 次提交
  53. 13 9月, 2011 1 次提交
  55. 08 9月, 2011 1 次提交
    • P
      posix-cpu-timers: Cure SMP accounting oddities · e8abccb7
      由 Peter Zijlstra 提交于 
      David reported:

  Attached below is a watered-down version of rt/tst-cpuclock2.c from
  GLIBC.  Just build it with "gcc -o test test.c -lpthread -lrt" or
  similar.

  Run it several times, and you will see cases where the main thread
  will measure a process clock difference before and after the nanosleep
  which is smaller than the cpu-burner thread's individual thread clock
  difference.  This doesn't make any sense since the cpu-burner thread
  is part of the top-level process's thread group.

  I've reproduced this on both x86-64 and sparc64 (using both 32-bit and
  64-bit binaries).

  For example:

  [davem@boricha build-x86_64-linux]$ ./test
  process: before(0.001221967) after(0.498624371) diff(497402404)
  thread:  before(0.000081692) after(0.498316431) diff(498234739)
  self:    before(0.001223521) after(0.001240219) diff(16698)
  [davem@boricha build-x86_64-linux]$

  The diff of 'process' should always be >= the diff of 'thread'.

  I make sure to wrap the 'thread' clock measurements the most tightly
  around the nanosleep() call, and that the 'process' clock measurements
  are the outer-most ones.

  ---
  #include <unistd.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include <time.h>
  #include <fcntl.h>
  #include <string.h>
  #include <errno.h>
  #include <pthread.h>

  static pthread_barrier_t barrier;

  static void *chew_cpu(void *arg)
  {
	  pthread_barrier_wait(&barrier);
	  while (1)
		  __asm__ __volatile__("" : : : "memory");
	  return NULL;
  }

  int main(void)
  {
	  clockid_t process_clock, my_thread_clock, th_clock;
	  struct timespec process_before, process_after;
	  struct timespec me_before, me_after;
	  struct timespec th_before, th_after;
	  struct timespec sleeptime;
	  unsigned long diff;
	  pthread_t th;
	  int err;

	  err = clock_getcpuclockid(0, &process_clock);
	  if (err)
		  return 1;

	  err = pthread_getcpuclockid(pthread_self(), &my_thread_clock);
	  if (err)
		  return 1;

	  pthread_barrier_init(&barrier, NULL, 2);
	  err = pthread_create(&th, NULL, chew_cpu, NULL);
	  if (err)
		  return 1;

	  err = pthread_getcpuclockid(th, &th_clock);
	  if (err)
		  return 1;

	  pthread_barrier_wait(&barrier);

	  err = clock_gettime(process_clock, &process_before);
	  if (err)
		  return 1;

	  err = clock_gettime(my_thread_clock, &me_before);
	  if (err)
		  return 1;

	  err = clock_gettime(th_clock, &th_before);
	  if (err)
		  return 1;

	  sleeptime.tv_sec = 0;
	  sleeptime.tv_nsec = 500000000;
	  nanosleep(&sleeptime, NULL);

	  err = clock_gettime(th_clock, &th_after);
	  if (err)
		  return 1;

	  err = clock_gettime(my_thread_clock, &me_after);
	  if (err)
		  return 1;

	  err = clock_gettime(process_clock, &process_after);
	  if (err)
		  return 1;

	  diff = process_after.tv_nsec - process_before.tv_nsec;
	  printf("process: before(%lu.%.9lu) after(%lu.%.9lu) diff(%lu)\n",
		 process_before.tv_sec, process_before.tv_nsec,
		 process_after.tv_sec, process_after.tv_nsec, diff);
	  diff = th_after.tv_nsec - th_before.tv_nsec;
	  printf("thread:  before(%lu.%.9lu) after(%lu.%.9lu) diff(%lu)\n",
		 th_before.tv_sec, th_before.tv_nsec,
		 th_after.tv_sec, th_after.tv_nsec, diff);
	  diff = me_after.tv_nsec - me_before.tv_nsec;
	  printf("self:    before(%lu.%.9lu) after(%lu.%.9lu) diff(%lu)\n",
		 me_before.tv_sec, me_before.tv_nsec,
		 me_after.tv_sec, me_after.tv_nsec, diff);

	  return 0;
  }

This is due to us using p->se.sum_exec_runtime in
thread_group_cputime() where we iterate the thread group and sum all
data. This does not take time since the last schedule operation (tick
or otherwise) into account. We can cure this by using
task_sched_runtime() at the cost of having to take locks.

This also means we can (and must) do away with
thread_group_sched_runtime() since the modified thread_group_cputime()
is now more accurate and would deadlock when called from
thread_group_sched_runtime().
Reported-by: NDavid Miller <davem@davemloft.net>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1314874459.7945.22.camel@twins
Cc: stable@kernel.org
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      e8abccb7
  57. 14 8月, 2011 1 次提交