Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759217AbbLBSm0 (ORCPT ); Wed, 2 Dec 2015 13:42:26 -0500 Received: from g2t4622.austin.hp.com ([15.73.212.79]:35590 "EHLO g2t4622.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757565AbbLBSmI (ORCPT ); Wed, 2 Dec 2015 13:42:08 -0500 From: Waiman Long To: Ingo Molnar , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Yuyang Du , Paul Turner , Ben Segall , Morten Rasmussen , Scott J Norton , Douglas Hatch , 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 Message-Id: <1449081710-20185-4-git-send-email-Waiman.Long@hpe.com> X-Mailer: git-send-email 1.7.1 In-Reply-To: <1449081710-20185-1-git-send-email-Waiman.Long@hpe.com> References: <1449081710-20185-1-git-send-email-Waiman.Long@hpe.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1611 Lines: 41 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 --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/