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,URIBL_BLOCKED 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 3919BC433B4 for ; Mon, 19 Apr 2021 10:04:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C634060E08 for ; Mon, 19 Apr 2021 10:04:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237989AbhDSKEg (ORCPT ); Mon, 19 Apr 2021 06:04:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43504 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231990AbhDSKEf (ORCPT ); Mon, 19 Apr 2021 06:04:35 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DAC27C06174A for ; Mon, 19 Apr 2021 03:04:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=FK9hdoxUBF8nPujcTiXlMmfbOgCpUz5UFCS8Vw7GCMQ=; b=AEAmanYdHkEVqoMlSg3fqsqaGN qw7InlSK5CtUpWRhi8fgOY0+yc4NlTrzZnqRqDkMmFRVfzASv3kUxPFoGupBtCBuKwzpWpxN7z5ze otxAq2JMTV300jz/8XKpSZPu+/xWJz4faX3Aje7PpPuXep15tjbFR7ywdX8IR5hnsSnLaVhlnBPUH 6oHeCGIiCe2UMLUISyTSbh1tdjCsGUaQxoIu/lxJ6T1cS44Qtx3Lt7kpNi+WciNiUh+JXo1lzI2gv 8//kw1bahb89A/hy58+ccaeanXYg0xyHgme6zaSV1rzmLsQlHqWXj5o6peJ+ncxsAdrgH59UqvedX WoQcntbA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1lYQk7-00DZK7-Kl; Mon, 19 Apr 2021 10:03:08 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 40E52300212; Mon, 19 Apr 2021 12:02:57 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id F090E2C23A969; Mon, 19 Apr 2021 12:02:56 +0200 (CEST) Date: Mon, 19 Apr 2021 12:02:56 +0200 From: Peter Zijlstra To: Rik van Riel Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Mel Gorman Subject: Re: [PATCH] sched,fair: skip newidle_balance if a wakeup is pending Message-ID: References: <20210418221751.7edfc03b@imladris.surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210418221751.7edfc03b@imladris.surriel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Apr 18, 2021 at 10:17:51PM -0400, Rik van Riel wrote: > The try_to_wake_up function has an optimization where it can queue > a task for wakeup on its previous CPU, if the task is still in the > middle of going to sleep inside schedule(). > > Once schedule() re-enables IRQs, the task will be woken up with an > IPI, and placed back on the runqueue. > > If we have such a wakeup pending, there is no need to search other > CPUs for runnable tasks. Just skip (or bail out early from) newidle > balancing, and run the just woken up task. > > For a memcache like workload test, this reduces total CPU use by > about 2%, proportionally split between user and system time, > and p99 and p95 application response time by 2-3% on average. > The schedstats run_delay number shows a similar improvement. Nice. > Signed-off-by: Rik van Riel > --- > kernel/sched/fair.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 69680158963f..19a92c48939f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -7163,6 +7163,14 @@ done: __maybe_unused; > if (!rf) > return NULL; > > + /* > + * We have a woken up task pending here. No need to search for ones > + * elsewhere. This task will be enqueued the moment we unblock irqs > + * upon exiting the scheduler. > + */ > + if (rq->ttwu_pending) > + return NULL; As reported by the robot, that needs an CONFIG_SMP guard of sorts, #ifdef might work I suppose. > new_tasks = newidle_balance(rq, rf); > > /* > @@ -10661,7 +10669,8 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) > * Stop searching for tasks to pull if there are > * now runnable tasks on this rq. > */ > - if (pulled_task || this_rq->nr_running > 0) > + if (pulled_task || this_rq->nr_running > 0 || > + this_rq->ttwu_pending) Either cino=(0:0 or just bust the limit and make it 84 chars.