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authorJason Low <jason.low2@hp.com>2014-09-02 00:41:24 -0700
committerIngo Molnar <mingo@kernel.org>2014-09-09 06:47:29 +0200
commit8236d907ab3411ad452280faa8b26c1347327380 (patch)
tree54955da72837f14cdeb0de54878988ab29b930e7 /kernel/sched/fair.c
parent5cd038f53ed9ec7a17ab7d536a727363080f4210 (diff)
sched: Reduce contention in update_cfs_rq_blocked_load()
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 <bsegall@google.com> Reviewed-by: Waiman Long <Waiman.Long@hp.com> Signed-off-by: Jason Low <jason.low2@hp.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Paul Turner <pjt@google.com> Cc: jason.low2@hp.com Cc: Yuyang Du <yuyang.du@intel.com> Cc: Aswin Chandramouleeswaran <aswin@hp.com> Cc: Chegu Vinod <chegu_vinod@hp.com> Cc: Scott J Norton <scott.norton@hp.com> Cc: Tim Chen <tim.c.chen@linux.intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1409643684.19197.15.camel@j-VirtualBox Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched/fair.c')
-rw-r--r--kernel/sched/fair.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 50d2025c1777..be9e97b0d76f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -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;