Commit-ID: 8236d907ab3411ad452280faa8b26c1347327380
Gitweb: http://git.kernel.org/tip/8236d907ab3411ad452280faa8b26c1347327380
Author: Jason Low <jason.low2@xxxxxx>
AuthorDate: Tue, 2 Sep 2014 00:41:24 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 9 Sep 2014 06:47:29 +0200
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@xxxxxxxxxx>
Reviewed-by: Waiman Long <Waiman.Long@xxxxxx>
Signed-off-by: Jason Low <jason.low2@xxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: jason.low2@xxxxxx
Cc: Yuyang Du <yuyang.du@xxxxxxxxx>
Cc: Aswin Chandramouleeswaran <aswin@xxxxxx>
Cc: Chegu Vinod <chegu_vinod@xxxxxx>
Cc: Scott J Norton <scott.norton@xxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1409643684.19197.15.camel@j-VirtualBox
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/fair.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 50d2025..be9e97b 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;
--
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