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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,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 C65E4C433DB for ; Tue, 23 Mar 2021 13:46:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 87FFF619B3 for ; Tue, 23 Mar 2021 13:46:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230406AbhCWNp6 (ORCPT ); Tue, 23 Mar 2021 09:45:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39098 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231745AbhCWNpL (ORCPT ); Tue, 23 Mar 2021 09:45:11 -0400 Received: from mail-lj1-x231.google.com (mail-lj1-x231.google.com [IPv6:2a00:1450:4864:20::231]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E3E37C061574 for ; Tue, 23 Mar 2021 06:45:10 -0700 (PDT) Received: by mail-lj1-x231.google.com with SMTP id f26so25680757ljp.8 for ; Tue, 23 Mar 2021 06:45:10 -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=W0UisNNbKbH6zzHCd8e8U+xHlLwMetDgdknX46c/dSs=; b=Nrzj1L7LOc078mFYMTtGNGLlJQdveIC2drIRxtWTtJC9IlAUaf/C5dTOSFswcG1S1l r8P6pW3bhUiwYJIYfdiXlayJUn7VqAdvlNVedSJxdK7fT/pLDHdBNktbXdNFrun0cz9Z TthKlCwPDlGhdn3B/kChAr65LQvEXYf4QejpC7PZVWOoE6K7tTXHIi4GxFJDv/0cVcZL MnNxpDLDqLZ4cvYY8xw0LEDYB6eFsqiJIlqPFSBrMO1OM13YkcDrNYw/0JvW1pMrhcrv NwLkq7ANNiT8ZzUisXxG2Bxoem9luljDoZtNFqKz/CLO10bpXt0t7Ph3jcY/8Ifugiru zgNg== 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=W0UisNNbKbH6zzHCd8e8U+xHlLwMetDgdknX46c/dSs=; b=OIkh+1Lnzl5In4HC8IPnc0FKB1k+y7B8QfGKrIBO7UGRmmlnKNv5qjMW6KTJzEQnNM CzEZmzIs+zP1aYOb71fMK/P9st2l9Vl33ANVXcbDppqdJavUwaJRW1+FYJAtCRDScXaN DyYptL/dDOmVohf3LrgN8kdgeGMf40GFrHRLg5N4cbkhz6xwkR3uqPuE8pTHM5dQ/+Vp xQMZu8s5zxyq5I7OLzLiDK9h2DcT51FG/GJqlC/pTWx1cVN3cBsOzwn8A04idZHhkHK+ xDymFf+Ip+U0T6vKyyHmUM4m4wzi7EdZu9c2OiStr1yrbdI0wYNjyeU8NRZqoWvdF8eI IO7g== X-Gm-Message-State: AOAM531n/0jymZw+mX+gfHW5Ut1oa3uMpHIOebd3XyxKujMmNODP/yDD l9fnFKO8b++pRdiVZn7Czhc+MS1jDD/ZTTUqS1gMjA== X-Google-Smtp-Source: ABdhPJxLzsIFJqewS2UGeikJEOK5IUe7eAtO/0IDM3RG94kNNKWanslXjWKK5ZNWo7u8W2dGmzs7qcMwdGQF5wKqF/w= X-Received: by 2002:a2e:5315:: with SMTP id h21mr3085264ljb.299.1616507109311; Tue, 23 Mar 2021 06:45:09 -0700 (PDT) MIME-Version: 1.0 References: <1614154549-116078-1-git-send-email-aubrey.li@intel.com> <74f65436-09f2-a4f0-345f-8887b11a51bf@linux.intel.com> In-Reply-To: <74f65436-09f2-a4f0-345f-8887b11a51bf@linux.intel.com> From: Vincent Guittot Date: Tue, 23 Mar 2021 14:44:57 +0100 Message-ID: Subject: Re: [PATCH v2] sched/fair: reduce long-tail newly idle balance cost To: "Li, Aubrey" Cc: Aubrey Li , Ingo Molnar , Peter Zijlstra , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , linux-kernel , Andi Kleen , Tim Chen , Srinivas Pandruvada , "Rafael J . Wysocki" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Aurey, On Tue, 16 Mar 2021 at 05:27, Li, Aubrey wrote: > > On 2021/2/24 16:15, Aubrey Li wrote: > > A long-tail load balance cost is observed on the newly idle path, > > this is caused by a race window between the first nr_running check > > of the busiest runqueue and its nr_running recheck in detach_tasks. > > > > Before the busiest runqueue is locked, the tasks on the busiest > > runqueue could be pulled by other CPUs and nr_running of the busiest > > runqueu becomes 1 or even 0 if the running task becomes idle, this > > causes detach_tasks breaks with LBF_ALL_PINNED flag set, and triggers > > load_balance redo at the same sched_domain level. > > > > In order to find the new busiest sched_group and CPU, load balance will > > recompute and update the various load statistics, which eventually leads > > to the long-tail load balance cost. > > > > This patch clears LBF_ALL_PINNED flag for this race condition, and hence > > reduces the long-tail cost of newly idle balance. > > Ping... Reviewed-by: Vincent Guittot > > > > > Cc: Vincent Guittot > > Cc: Mel Gorman > > Cc: Andi Kleen > > Cc: Tim Chen > > Cc: Srinivas Pandruvada > > Cc: Rafael J. Wysocki > > Signed-off-by: Aubrey Li > > --- > > kernel/sched/fair.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 04a3ce2..5c67804 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -7675,6 +7675,15 @@ static int detach_tasks(struct lb_env *env) > > > > lockdep_assert_held(&env->src_rq->lock); > > > > + /* > > + * Source run queue has been emptied by another CPU, clear > > + * LBF_ALL_PINNED flag as we will not test any task. > > + */ > > + if (env->src_rq->nr_running <= 1) { > > + env->flags &= ~LBF_ALL_PINNED; > > + return 0; > > + } > > + > > if (env->imbalance <= 0) > > return 0; > > > > >