diff options
| author |   Peter Zijlstra <peterz@infradead.org> | 2013-11-11 18:21:56 +0100 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2013-11-13 13:33:54 +0100 |
| commit | 911b2898b3c9fe0048e9485ad1629ed4fce330fd (patch) | |
| tree | b430d3ef975f60b4c19caf211ea025cc4fa173a1 /kernel | |
| parent | sched/numa: Cure update_numa_stats() vs. hotplug (diff) | |
| download | linux-dev-911b2898b3c9fe0048e9485ad1629ed4fce330fd.tar.xz linux-dev-911b2898b3c9fe0048e9485ad1629ed4fce330fd.zip | |
sched: Optimize task_sched_runtime()
Large multi-threaded apps like to hit this using do_sys_times() and
then queue up on the rq->lock.
Avoid when possible.
Larry reported ~20% performance increase his test case.
Reported-by: Larry Woodman <lwoodman@redhat.com>
Suggested-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20131111172925.GG26898@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/core.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 1deccd78be98..c1808606ee5f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2253,6 +2253,20 @@ unsigned long long task_sched_runtime(struct task_struct *p) struct rq *rq; u64 ns = 0; +#if defined(CONFIG_64BIT) && defined(CONFIG_SMP) + /* + * 64-bit doesn't need locks to atomically read a 64bit value. + * So we have a optimization chance when the task's delta_exec is 0. + * Reading ->on_cpu is racy, but this is ok. + * + * If we race with it leaving cpu, we'll take a lock. So we're correct. + * If we race with it entering cpu, unaccounted time is 0. This is + * indistinguishable from the read occurring a few cycles earlier. + */ + if (!p->on_cpu) + return p->se.sum_exec_runtime; +#endif + rq = task_rq_lock(p, &flags); ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq); task_rq_unlock(rq, p, &flags); |