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  1. 09 12月, 2009 1 次提交
  3. 24 11月, 2009 1 次提交
    • T
      sched: Optimize branch hint in pick_next_task_fair() · 36ace27e
      由 Tim Blechmann 提交于 
      Branch hint profiling on my nehalem machine showed 90%
incorrect branch hints:

  15728471 158903754  90 pick_next_task_fair
  sched_fair.c    1555
Signed-off-by: NTim Blechmann <tim@klingt.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4B0BBBB1.2050100@klingt.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      36ace27e
  5. 13 11月, 2009 2 次提交
  7. 05 11月, 2009 2 次提交
    • M
      sched: Fix affinity logic in select_task_rq_fair() · fd210738
      由 Mike Galbraith 提交于 
      Ingo Molnar reported:

[   26.804000] BUG: using smp_processor_id() in preemptible [00000000] code: events/1/10
[   26.808000] caller is vmstat_update+0x26/0x70
[   26.812000] Pid: 10, comm: events/1 Not tainted 2.6.32-rc5 #6887
[   26.816000] Call Trace:
[   26.820000]  [<c1924a24>] ? printk+0x28/0x3c
[   26.824000]  [<c13258a0>] debug_smp_processor_id+0xf0/0x110
[   26.824000] mount used greatest stack depth: 1464 bytes left
[   26.828000]  [<c111d086>] vmstat_update+0x26/0x70
[   26.832000]  [<c1086418>] worker_thread+0x188/0x310
[   26.836000]  [<c10863b7>] ? worker_thread+0x127/0x310
[   26.840000]  [<c108d310>] ? autoremove_wake_function+0x0/0x60
[   26.844000]  [<c1086290>] ? worker_thread+0x0/0x310
[   26.848000]  [<c108cf0c>] kthread+0x7c/0x90
[   26.852000]  [<c108ce90>] ? kthread+0x0/0x90
[   26.856000]  [<c100c0a7>] kernel_thread_helper+0x7/0x10
[   26.860000] BUG: using smp_processor_id() in preemptible [00000000] code: events/1/10
[   26.864000] caller is vmstat_update+0x3c/0x70

Because this commit:

  a1f84a3a: sched: Check for an idle shared cache in select_task_rq_fair()

broke ->cpus_allowed.
Signed-off-by: NMike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: arjan@infradead.org
Cc: <stable@kernel.org>
LKML-Reference: <1257415066.12867.1.camel@marge.simson.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      fd210738
    • M
      sched: Check for an idle shared cache in select_task_rq_fair() · a1f84a3a
      由 Mike Galbraith 提交于 
      When waking affine, check for an idle shared cache, and if
found, wake to that CPU/sibling instead of the waker's CPU.

This improves pgsql+oltp ramp up by roughly 8%. Possibly more
for other loads, depending on overlap. The trade-off is a
roughly 1% peak downturn if tasks are truly synchronous.
Signed-off-by: NMike Galbraith <efault@gmx.de>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@kernel.org>
LKML-Reference: <1256654138.17752.7.camel@marge.simson.net>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      a1f84a3a
  9. 24 10月, 2009 1 次提交
    • M
      sched: Strengthen buddies and mitigate buddy induced latencies · f685ceac
      由 Mike Galbraith 提交于 
      This patch restores the effectiveness of LAST_BUDDY in preventing
pgsql+oltp from collapsing due to wakeup preemption. It also
switches LAST_BUDDY to exclusively do what it does best, namely
mitigate the effects of aggressive wakeup preemption, which
improves vmark throughput markedly, and restores mysql+oltp
scalability.

Since buddies are about scalability, enable them beginning at the
point where we begin expanding sched_latency, namely
sched_nr_latency. Previously, buddies were cleared aggressively,
which seriously reduced their effectiveness. Not clearing
aggressively however, produces a small drop in mysql+oltp
throughput immediately after peak, indicating that LAST_BUDDY is
actually doing some harm. This is right at the point where X on the
desktop in competition with another load wants low latency service.
Ergo, do not enable until we need to scale.

To mitigate latency induced by buddies, or by a task just missing
wakeup preemption, check latency at tick time.

Last hunk prevents buddies from stymieing BALANCE_NEWIDLE via
CACHE_HOT_BUDDY.

Supporting performance tests:

 tip   = v2.6.32-rc5-1497-ga525b32
 tipx  = NO_GENTLE_FAIR_SLEEPERS NEXT_BUDDY granularity knobs = 31 knobs + 31 buddies
 tip+x = NO_GENTLE_FAIR_SLEEPERS granularity knobs = 31 knobs

(Three run averages except where noted.)

 vmark:
 ------
 tip           108466 messages per second
 tip+          125307 messages per second
 tip+x         125335 messages per second
 tipx          117781 messages per second
 2.6.31.3      122729 messages per second

 mysql+oltp:
 -----------
 clients          1        2        4        8       16       32       64        128    256
 ..........................................................................................
 tip        9949.89 18690.20 34801.24 34460.04 32682.88 30765.97 28305.27 25059.64 19548.08
 tip+      10013.90 18526.84 34900.38 34420.14 33069.83 32083.40 30578.30 28010.71 25605.47
 tipx       9698.71 18002.70 34477.56 33420.01 32634.30 31657.27 29932.67 26827.52 21487.18
 2.6.31.3   8243.11 18784.20 34404.83 33148.38 31900.32 31161.90 29663.81 25995.94 18058.86

 pgsql+oltp:
 -----------
 clients          1        2        4        8       16       32       64      128      256
 ..........................................................................................
 tip       13686.37 26609.25 51934.28 51347.81 49479.51 45312.65 36691.91 26851.57 24145.35
 tip+ (1x) 13907.85 27135.87 52951.98 52514.04 51742.52 50705.43 49947.97 48374.19 46227.94
 tip+x     13906.78 27065.81 52951.19 52542.59 52176.11 51815.94 50838.90 49439.46 46891.00
 tipx      13742.46 26769.81 52351.99 51891.73 51320.79 50938.98 50248.65 48908.70 46553.84
 2.6.31.3  13815.35 26906.46 52683.34 52061.31 51937.10 51376.80 50474.28 49394.47 47003.25
Signed-off-by: NMike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      f685ceac
  11. 14 10月, 2009 1 次提交
    • P
      sched: Do less agressive buddy clearing · 92f6a5e3
      由 Peter Zijlstra 提交于 
      Yanmin reported a hackbench regression due to:

 > commit de69a80b
 > Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
 > Date:   Thu Sep 17 09:01:20 2009 +0200
 >
 >     sched: Stop buddies from hogging the system

I really liked de69a80b, and it affecting hackbench shows I wasn't
crazy ;-)

So hackbench is a multi-cast, with one sender spraying multiple
receivers, who in their turn don't spray back.

This would be exactly the scenario that patch 'cures'. Previously
we would not clear the last buddy after running the next task,
allowing the sender to get back to work sooner than it otherwise
ought to have been, increasing latencies for other tasks.

Now, since those receivers don't poke back, they don't enforce the
buddy relation, which means there's nothing to re-elect the sender.

Cure this by less agressively clearing the buddy stats. Only clear
buddies when they were not chosen. It should still avoid a buddy
sticking around long after its served its time.
Reported-by: N"Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
CC: Mike Galbraith <efault@gmx.de>
LKML-Reference: <1255084986.8802.46.camel@laptop>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      92f6a5e3
  13. 24 9月, 2009 1 次提交
  15. 21 9月, 2009 1 次提交
  17. 19 9月, 2009 1 次提交
  19. 18 9月, 2009 1 次提交
  21. 17 9月, 2009 3 次提交
    • P
      sched: Fix SD_POWERSAVING_BALANCE|SD_PREFER_LOCAL vs SD_WAKE_AFFINE · 29cd8bae
      由 Peter Zijlstra 提交于 
      The SD_POWERSAVING_BALANCE|SD_PREFER_LOCAL code can break out of
the domain iteration early, making us miss the SD_WAKE_AFFINE bits.

Fix this by continuing iteration until there is no need for a
larger domain.

This also cleans up the cgroup stuff a bit, but not having two
update_shares() invocations.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      29cd8bae
    • P
      sched: Stop buddies from hogging the system · de69a80b
      由 Peter Zijlstra 提交于 
      Clear buddies more agressively.

The (theoretical, haven't actually observed any of this) problem is
that when we do not select either buddy in pick_next_entity()
because they are too far ahead of the left-most task, we do not
clear the buddies.

This means that as soon as we service the left-most task, these
same buddies will be tried again on the next schedule. Now if the
left-most task was a pure hog, it wouldn't have done any wakeups
and it wouldn't have set buddies of its own. That leads to the old
buddies dominating, which would lead to bad latencies.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      de69a80b
    • P
      sched: Add new wakeup preemption mode: WAKEUP_RUNNING · ad4b78bb
      由 Peter Zijlstra 提交于 
      Create a new wakeup preemption mode, preempt towards tasks that run
shorter on avg. It sets next buddy to be sure we actually run the task
we preempted for.

Test results:

 root@twins:~# while :; do :; done &
 [1] 6537
 root@twins:~# while :; do :; done &
 [2] 6538
 root@twins:~# while :; do :; done &
 [3] 6539
 root@twins:~# while :; do :; done &
 [4] 6540

 root@twins:/home/peter# ./latt -c4 sleep 4
 Entries: 48 (clients=4)

 Averages:
 ------------------------------
        Max          4750 usec
        Avg           497 usec
        Stdev         737 usec

 root@twins:/home/peter# echo WAKEUP_RUNNING > /debug/sched_features

 root@twins:/home/peter# ./latt -c4 sleep 4
 Entries: 48 (clients=4)

 Averages:
 ------------------------------
        Max            14 usec
        Avg             5 usec
        Stdev           3 usec

Disabled by default - needs more testing.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: NMike Galbraith <efault@gmx.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
LKML-Reference: <new-submission>
      ad4b78bb
  23. 16 9月, 2009 6 次提交
  25. 15 9月, 2009 12 次提交
  27. 14 9月, 2009 1 次提交
    • I
      perf_counter, sched: Add sched_stat_runtime tracepoint · f977bb49
      由 Ingo Molnar 提交于 
      This allows more precise tracking of how the scheduler accounts
(and acts upon) a task having spent N nanoseconds of CPU time.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      f977bb49
  29. 11 9月, 2009 1 次提交
    • I
      sched: Fix sched::sched_stat_wait tracepoint field · e1f84508
      由 Ingo Molnar 提交于 
      This weird perf trace output:

  cc1-9943  [001]  2802.059479616: sched_stat_wait: task: as:9944 wait: 2801938766276 [ns]

Is caused by setting one component field of the delta to zero
a bit too early. Move it to later.

( Note, this does not affect the NEW_FAIR_SLEEPERS interactivity bug,
  it's just a reporting bug in essence. )
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Nikos Chantziaras <realnc@arcor.de>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <4AA93D34.8040500@arcor.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      e1f84508
  31. 09 9月, 2009 2 次提交
  33. 08 9月, 2009 3 次提交
    • M
      sched: Ensure that a child can't gain time over it's parent after fork() · b5d9d734
      由 Mike Galbraith 提交于 
      A fork/exec load is usually "pass the baton", so the child
should never be placed behind the parent.  With START_DEBIT we
make room for the new task, but with child_runs_first, that
room comes out of the _parent's_ hide. There's nothing to say
that the parent wasn't ahead of min_vruntime at fork() time,
which means that the "baton carrier", who is essentially the
parent in drag, can gain time and increase scheduling latencies
for waiters.

With NEW_FAIR_SLEEPERS + START_DEBIT + child_runs_first
enabled, we essentially pass the sleeper fairness off to the
child, which is fine, but if we don't base placement on the
parent's updated vruntime, we can end up compounding latency
woes if the child itself then does fork/exec.  The debit
incurred at fork doesn't hurt the parent who is then going to
sleep and maybe exit, but the child who acquires the error
harms all comers.

This improves latencies of make -j<n> kernel build workloads.
Reported-by: NJens Axboe <jens.axboe@oracle.com>
Signed-off-by: NMike Galbraith <efault@gmx.de>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      b5d9d734
    • P
      sched: Deal with low-load in wake_affine() · 71a29aa7
      由 Peter Zijlstra 提交于 
      wake_affine() would always fail under low-load situations where
both prev and this were idle, because adding a single task will
always be a significant imbalance, even if there's nothing
around that could balance it.

Deal with this by allowing imbalance when there's nothing you
can do about it.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      71a29aa7
    • P
      sched: Remove short cut from select_task_rq_fair() · cdd2ab3d
      由 Peter Zijlstra 提交于 
      select_task_rq_fair() incorrectly skips the wake_affine()
logic, remove this.

When prev_cpu == this_cpu, the code jumps straight to the
wake_idle() logic, this doesn't give the wake_affine() logic
the chance to pin the task to this cpu.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
      cdd2ab3d