Commit-ID: aa0b7ae06387d40a988ce16a189082dee6e570bc
Gitweb: http://git.kernel.org/tip/aa0b7ae06387d40a988ce16a189082dee6e570bc
Author: Waiman Long <Waiman.Long@xxxxxxx>
AuthorDate: Wed, 2 Dec 2015 13:41:50 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 4 Dec 2015 10:34:49 +0100
sched/fair: Disable the task group load_avg update for the root_task_group
Currently, the update_tg_load_avg() function attempts to update the
tg's load_avg value whenever the load changes even for root_task_group
where the load_avg value will never be used. This patch will disable
the load_avg update when the given task group is the root_task_group.
Running a Java benchmark with noautogroup and a 4.3 kernel on a
16-socket IvyBridge-EX system, the amount of CPU time (as reported by
perf) consumed by task_tick_fair() which includes update_tg_load_avg()
decreased from 0.71% to 0.22%, a more than 3X reduction. The Max-jOPs
results also increased slightly from 983015 to 986449.
Signed-off-by: Waiman Long <Waiman.Long@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Douglas Hatch <doug.hatch@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Morten Rasmussen <morten.rasmussen@xxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Scott J Norton <scott.norton@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Yuyang Du <yuyang.du@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1449081710-20185-4-git-send-email-Waiman.Long@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/fair.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4b0e8b8..1093873 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2709,6 +2709,12 @@ static inline void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
{
long delta = cfs_rq->avg.load_avg - cfs_rq->tg_load_avg_contrib;
+ /*
+ * No need to update load_avg for root_task_group as it is not used.
+ */
+ if (cfs_rq->tg == &root_task_group)
+ return;
+
if (force || abs(delta) > cfs_rq->tg_load_avg_contrib / 64) {
atomic_long_add(delta, &cfs_rq->tg->load_avg);
cfs_rq->tg_load_avg_contrib = cfs_rq->avg.load_avg;
--
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