Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH v2 3/3] sched/fair: Disable tg load_avg update for root_task_group | Date | Wed, 2 Dec 2015 13:41:50 -0500 |
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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@hpe.com> --- kernel/sched/fair.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8f1eccc..4607cb7 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2670,6 +2670,12 @@ 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; -- 1.7.1
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