From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 50570C433DF for ; Mon, 15 Jun 2020 15:10:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2D0F320739 for ; Mon, 15 Jun 2020 15:10:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="vRNGuRQZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730878AbgFOPKI (ORCPT ); Mon, 15 Jun 2020 11:10:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729875AbgFOPKG (ORCPT ); Mon, 15 Jun 2020 11:10:06 -0400 Received: from mail-lj1-x244.google.com (mail-lj1-x244.google.com [IPv6:2a00:1450:4864:20::244]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2F96CC061A0E for ; Mon, 15 Jun 2020 08:10:05 -0700 (PDT) Received: by mail-lj1-x244.google.com with SMTP id x18so19592876lji.1 for ; Mon, 15 Jun 2020 08:10:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=P4sVMM7TaNawdbsHgDCWa8zSnS2h9z0AXuq8X1e8ReQ=; b=vRNGuRQZjesjUflGiRKEGce7m37DbhtoGaMt5c9miL80zJacRgCqaFj88HlLnKbQZV VThb+a3WLwphv0AzeTjNvjFY1u/sWfwGUhD/fd6EZVWdMajCACk8nKx5LeR6TZuSduTR Ow5p1T9ltleg2ul7/5H0fCYq6apXcTA9xI+15VzOF5tfGIgZ7CjAB5IV/GN/CwgkUhFc tjPailaxNrN8SAkwNPqgg8rChdsY/DmP/vX+wkjMHXed5NNTL/YgtTUiCSoM5WayfNyU HY+3096zEW3bTBWeBGIrIe88rL6tvhYldzO1OtRX0iXIYNh0Nr3SKW4JAKKHnDM5c5Sv F76w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=P4sVMM7TaNawdbsHgDCWa8zSnS2h9z0AXuq8X1e8ReQ=; b=KtIkczNgv8QINYpfurbWXuf0Px6P2CzmnaulWtBbD8l9MtVH64uHgfbgExKwrqErQB 5mS2D24bZ6IQYl1aCa6i67pSKNcc7u2WjD4Otc5r4wlD1n0GdoRyk0N925UNpMA8Fg5o cAePIFGFzfi1wL3OVyPND9Cq0imau8t6NrIwdo1ro7fSr8+PQ9spGshXqrIfeL/Q5jeU 5eFu8ZY+BmOM2vGILirD8JfPLyo2pjY9HsMqP3ovsJbx8DmOK/VuVG39Irmz7LgFbbj9 JyCeDvue3aRlpamqr2RSzy65qutc8vJEZMUQKtyueiKgeYoMnHn+ahVaZLyjnZgeeR7v 2Asg== X-Gm-Message-State: AOAM532DA0NCpAeTrVhgVm0iUpZSjGl1ayBDhjCU6lnQIcoiYz1aDIL8 bUnLTUi/QqD0lLmkivQl9aNvmvgP/0KoDxGcdCCESA== X-Google-Smtp-Source: ABdhPJyq3PYE0aYlLV/tRtn7CGYlJGREOYSvNVsbKqAMu9OfeKFSvgRc1SIy1/QCP+5sVWnrNBoALXKqi0w6a4WFCWk= X-Received: by 2002:a2e:96da:: with SMTP id d26mr13367284ljj.25.1592233803627; Mon, 15 Jun 2020 08:10:03 -0700 (PDT) MIME-Version: 1.0 References: <6f2f195aea48bc50187dfb064aa530ba132be01b.1592230286.git.rocking@linux.alibaba.com> In-Reply-To: <6f2f195aea48bc50187dfb064aa530ba132be01b.1592230286.git.rocking@linux.alibaba.com> From: Vincent Guittot Date: Mon, 15 Jun 2020 17:09:51 +0200 Message-ID: Subject: Re: [PATCH] sched/fair: Optimize dequeue_task_fair() To: Peng Wang Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , linux-kernel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 15 Jun 2020 at 16:20, Peng Wang wrote: > > While looking at enqueue_task_fair and dequeue_task_fair, it occurred > to me that dequeue_task_fair can also be optimized as Vincent described > in commit 7d148be69e3a ("sched/fair: Optimize enqueue_task_fair()"). good point > > dequeue_throttle label can ensure se not to be NULL, and se is > always NULL when reaching root level. > > Signed-off-by: Peng Wang > --- > kernel/sched/fair.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index cbcb2f7..e6be952 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5614,10 +5614,10 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) > > } > > -dequeue_throttle: > - if (!se) > - sub_nr_running(rq, 1); > + /* At this point se is NULL and we are at root level*/ > + sub_nr_running(rq, 1); > > +dequeue_throttle: > /* balance early to pull high priority tasks */ > if (unlikely(!was_sched_idle && sched_idle_rq(rq))) > rq->next_balance = jiffies; You can move the label here because sched_idle_rq() uses rq->nr-running and rq->cfs.idle_h_nr_running so they will not change if we jump to the label before reaching root level > -- > 2.9.5 >