From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752052AbaAQO0w (ORCPT ); Fri, 17 Jan 2014 09:26:52 -0500 Received: from merlin.infradead.org ([205.233.59.134]:35330 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750937AbaAQO0u (ORCPT ); Fri, 17 Jan 2014 09:26:50 -0500 Date: Fri, 17 Jan 2014 15:26:44 +0100 From: Peter Zijlstra To: Daniel Lezcano Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, linaro-kernel@lists.linaro.org, alex.shi@linaro.org Subject: Re: [PATCH 4/4] sched: Idle task shortcut optimization Message-ID: <20140117142644.GI11314@laptop.programming.kicks-ass.net> References: <1389949444-14821-1-git-send-email-daniel.lezcano@linaro.org> <1389949444-14821-4-git-send-email-daniel.lezcano@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1389949444-14821-4-git-send-email-daniel.lezcano@linaro.org> 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 On Fri, Jan 17, 2014 at 10:04:04AM +0100, Daniel Lezcano wrote: > @@ -2679,11 +2715,8 @@ need_resched: > > pre_schedule(rq, prev); > > - if (unlikely(!rq->nr_running)) > - rq->idle_stamp = idle_balance(rq) ? 0 : rq_clock(rq); > - > put_prev_task(rq, prev); > - next = pick_next_task(rq); > + next = pick_next_task_or_idle(rq); > clear_tsk_need_resched(prev); > clear_preempt_need_resched(); > rq->skip_clock_update = 0; I have vague memories that we need to have idle_balance() before put_prev_task(), but I can't recollect why this would be so. That said, if I resurrect these patches: https://lkml.org/lkml/2012/6/14/271 I suppose we could write something like: struct task_struct *pick_next_task(struct rq *rq, struct task_struct *prev) { const struct sched_class *class; struct task_struct *p; again: if (likely(rq->nr_running)) { if (likely(rq->nr_running == rq->cfs.h_nr_running)) return fair_sched_class.pick_next_task(rq, prev); for_each_class(class) { p = class->pick_next_task(rq, prev); if (p) return p; } } if (idle_balance(rq)) goto again; rq->idle_stamp = rq_clock(rq); return idle_sched_class.pick_next_task(rq, prev); } Which keeps idle_balance() before put_prev_task(), and by using idle_sched_clas.pick_next_task() doesn't rape the idle class interface like you did :-)