Commit-ID: aa0b7ae06387d40a988ce16a189082dee6e570bc Gitweb: http://git.kernel.org/tip/aa0b7ae06387d40a988ce16a189082dee6e570bc Author: Waiman Long <[email protected]> AuthorDate: Wed, 2 Dec 2015 13:41:50 -0500 Committer: Ingo Molnar <[email protected]> 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 <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Reviewed-by: Ben Segall <[email protected]> Cc: Douglas Hatch <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Mike Galbraith <[email protected]> Cc: Morten Rasmussen <[email protected]> Cc: Paul Turner <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Scott J Norton <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Yuyang Du <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
