From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752456AbaAQPGu (ORCPT ); Fri, 17 Jan 2014 10:06:50 -0500 Received: from mail-we0-f177.google.com ([74.125.82.177]:44868 "EHLO mail-we0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751918AbaAQPGs (ORCPT ); Fri, 17 Jan 2014 10:06:48 -0500 Message-ID: <52D94705.1000407@linaro.org> Date: Fri, 17 Jan 2014 16:06:45 +0100 From: Daniel Lezcano User-Agent: Mozilla/5.0 (X11; Linux i686; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Peter Zijlstra 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 References: <1389949444-14821-1-git-send-email-daniel.lezcano@linaro.org> <1389949444-14821-4-git-send-email-daniel.lezcano@linaro.org> <20140117142644.GI11314@laptop.programming.kicks-ass.net> In-Reply-To: <20140117142644.GI11314@laptop.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/17/2014 03:26 PM, Peter Zijlstra wrote: > 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 :-) But put_prev_task is called before pick_next_task, so idle_balance() is called after now, no ? -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog