From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753767AbaHERxo (ORCPT ); Tue, 5 Aug 2014 13:53:44 -0400 Received: from g2t2352.austin.hp.com ([15.217.128.51]:13193 "EHLO g2t2352.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753363AbaHERxn (ORCPT ); Tue, 5 Aug 2014 13:53:43 -0400 Message-ID: <53E11A22.4070604@hp.com> Date: Tue, 05 Aug 2014 13:53:38 -0400 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Jason Low CC: Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, Ben Segall , Mel Gorman , Mike Galbraith , Rik van Riel , Aswin Chandramouleeswaran , Chegu Vinod , Scott J Norton Subject: Re: [PATCH] sched: Reduce contention in update_cfs_rq_blocked_load References: <1407184118.11407.11.camel@j-VirtualBox> In-Reply-To: <1407184118.11407.11.camel@j-VirtualBox> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/04/2014 04:28 PM, Jason Low wrote: > When running workloads on 2+ socket systems, based on perf profiles, the > update_cfs_rq_blocked_load function constantly shows up as taking up a > noticeable % of run time. This is especially apparent on an 8 socket > machine. For example, when running the AIM7 custom workload, we see: > > 4.18% reaim [kernel.kallsyms] [k] update_cfs_rq_blocked_load > > 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. In the above case, with the > patch, perf reports the total time spent in this function went down by more > than a factor of 3x: > > 1.18% reaim [kernel.kallsyms] [k] update_cfs_rq_blocked_load > > Signed-off-by: Jason Low > --- > kernel/sched/fair.c | 3 +++ > 1 files changed, 3 insertions(+), 0 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index bfa3c86..8d4cc72 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2377,6 +2377,9 @@ 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; Reviewed-by: Waiman Long