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sched: Reduce contention in update_cfs_rq_blocked_load()

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When running workloads on 2+ socket systems, based on perf profiles, the
update_cfs_rq_blocked_load() function often shows up as taking up a
noticeable % of run time.

Much of the contention is in __update_cfs_rq_tg_load_contrib() when we
update the tg load contribution stats.  However, it turns out that in many
cases, they don't need to be updated and "tg_contrib" is 0.

This patch adds a check in __update_cfs_rq_tg_load_contrib() to skip updating
tg load contribution stats when nothing needs to be updated. This reduces the
cacheline contention that would be unnecessary.

Reviewed-by: Ben Segall <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Signed-off-by: Jason Low <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Paul Turner <[email protected]>
Cc: [email protected]
Cc: Yuyang Du <[email protected]>
Cc: Aswin Chandramouleeswaran <[email protected]>
Cc: Chegu Vinod <[email protected]>
Cc: Scott J Norton <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: http://lkml.kernel.org/r/1409643684.19197.15.camel@j-VirtualBox
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Jason Low 2014-09-02 00:41:24 -07:00 • committed by Ingo Molnar
commit 8236d907ab
1 changed files with 3 additions and 0 deletions
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3
kernel/sched/fair.c
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@ -2382,6 +2382,9 @@ static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
tg_contrib = cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg;
tg_contrib -= cfs_rq->tg_load_contrib;
if (!tg_contrib)
return;
if (force_update || abs(tg_contrib) > cfs_rq->tg_load_contrib / 8) {
atomic_long_add(tg_contrib, &tg->load_avg);
cfs_rq->tg_load_contrib += tg_contrib;