Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756445Ab3IZJ6Y (ORCPT ); Thu, 26 Sep 2013 05:58:24 -0400 Received: from merlin.infradead.org ([205.233.59.134]:45732 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755712Ab3IZJ6W (ORCPT ); Thu, 26 Sep 2013 05:58:22 -0400 Date: Thu, 26 Sep 2013 11:58:12 +0200 From: Peter Zijlstra To: Mike Galbraith Cc: Ingo Molnar , Paul Turner , Rik van Riel , linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH] sched: Avoid select_idle_sibling() for wake_affine(.sync=true) Message-ID: <20130926095812.GR3081@twins.programming.kicks-ass.net> References: <20130925075341.GB3081@twins.programming.kicks-ass.net> <1380099377.8523.9.camel@marge.simpson.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1380099377.8523.9.camel@marge.simpson.net> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2772 Lines: 87 On Wed, Sep 25, 2013 at 10:56:17AM +0200, Mike Galbraith wrote: > That will make pipe-test go fugly -> pretty, and help very fast/light > localhost network, but eat heavier localhost overlap recovery. We need > a working (and cheap) overlap detector scheme, so we can know when there > is enough to be worth going after. We used to have an overlap detectoring thing.. It went away though. But see if you can make something like the below work? You could make it a general overlap thing and try without the sync too I suppose.. --- include/linux/sched.h | 3 +++ kernel/sched/fair.c | 25 +++++++++++++++++++++++++ 2 files changed, 28 insertions(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index b5344de..5428016 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -974,6 +974,9 @@ struct sched_entity { u64 vruntime; u64 prev_sum_exec_runtime; + u64 last_sync_wakeup; + u64 avg_overlap; + u64 nr_migrations; #ifdef CONFIG_SCHEDSTATS diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2b89cd2..47b0d0f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2913,6 +2913,17 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) struct sched_entity *se = &p->se; int task_sleep = flags & DEQUEUE_SLEEP; + if (se->last_sync_wakeup) { + u64 overlap; + s64 diff; + + overlap = rq->clock - se->last_sync_wakeup; + se->last_sync_wakeup = 0; + + diff = overlap - se->avg_overlap; + se->avg_overlap += diff >> 8; + } + for_each_sched_entity(se) { cfs_rq = cfs_rq_of(se); dequeue_entity(cfs_rq, se, flags); @@ -3429,6 +3440,9 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags) int want_affine = 0; int sync = wake_flags & WF_SYNC; + if (sync) + p->se.last_sync_wakeup = sched_clock_cpu(cpu); + if (p->nr_cpus_allowed == 1) return prev_cpu; @@ -3461,6 +3475,17 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags) if (cpu != prev_cpu && wake_affine(affine_sd, p, sync)) prev_cpu = cpu; + /* + * Don't bother with select_idle_sibling() in the case of a sync wakeup + * where we know the only running task will soon go-away. Going + * through select_idle_sibling will only lead to pointless ping-pong. + */ + if (sync && prev_cpu == cpu && cpu_rq(cpu)->nr_running == 1 && + current->se.avg_overlap < 10000) { + new_cpu = cpu; + goto unlock; + } + new_cpu = select_idle_sibling(p, prev_cpu); goto unlock; } -- 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/