Messages in this thread Patch in this message | | | Date | Thu, 27 Oct 2022 13:26:03 -0700 | Subject | [PATCH] sched: consider WF_SYNC to find idle siblings | From | Andrei Vagin <> |
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From: Andrei Vagin <avagin@gmail.com>
WF_SYNC means that the waker goes to sleep after wakeup, so the current cpu can be considered idle if the waker is the only process that is running on it.
The perf pipe benchmark shows that this change reduces the average time per operation from 8.8 usecs/op to 3.7 usecs/op.
Before: $ ./tools/perf/perf bench sched pipe # Running 'sched/pipe' benchmark: # Executed 1000000 pipe operations between two processes
Total time: 8.813 [sec]
8.813985 usecs/op 113456 ops/sec
After: $ ./tools/perf/perf bench sched pipe # Running 'sched/pipe' benchmark: # Executed 1000000 pipe operations between two processes
Total time: 3.743 [sec]
3.743971 usecs/op 267096 ops/sec
Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ben Segall <bsegall@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Valentin Schneider <vschneid@redhat.com> Signed-off-by: Andrei Vagin <avagin@gmail.com> --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e4a0b8bd941c..40ac3cc68f5b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7245,7 +7245,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag); } else if (wake_flags & WF_TTWU) { /* XXX always ? */ /* Fast path */ - new_cpu = select_idle_sibling(p, prev_cpu, new_cpu); + if (!sync || cpu != new_cpu || this_rq()->nr_running != 1) + new_cpu = select_idle_sibling(p, prev_cpu, new_cpu); } rcu_read_unlock(); -- 2.34.1
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