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 C36E7C433B4 for ; Wed, 14 Apr 2021 07:12:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 92D37613B1 for ; Wed, 14 Apr 2021 07:12:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349376AbhDNHNG (ORCPT ); Wed, 14 Apr 2021 03:13:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50736 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232540AbhDNHNA (ORCPT ); Wed, 14 Apr 2021 03:13:00 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A1953C061574 for ; Wed, 14 Apr 2021 00:12:39 -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=An14/uOqbqNoXgdc/38xhaX2pUyQaWxdG5rXPJLeQks=; b=TV5R9U9xdDbt7CRwEoSCyZYiOR Y+6nfwVug7s0CbXABCNGsc2/AA8WmS4YI+kgjzL1a90a+GI+CVMYQHfaErbZ/MQyZ+WkaHEQdEnGM LZNisTazY0LKtQknZbiC+7esPdaHta40rRZo8xWHCl9MVDjnY/HukwjHtK5Kp0oNNFRYO2OijElgI nrU09Wcdk8ZHhO91XMd3JEUN1Hq9uoCABhF4+M7dOSp0HfJSaiO/MYAKl6lDqJR1o3AMXk+zCr4IX keJEusjdBCJALm29e3UX/3vsNc6iXEmDYsase2JabqIghSUJliEoqF7tUYtlFVk3YvZ8aU22FPP/U 6epD1hxA==; 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 1lWZhF-006mws-Az; Wed, 14 Apr 2021 07:12:21 +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 94431300033; Wed, 14 Apr 2021 09:12:20 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7EED4203D395C; Wed, 14 Apr 2021 09:12:20 +0200 (CEST) Date: Wed, 14 Apr 2021 09:12:20 +0200 From: Peter Zijlstra To: qianjun.kernel@gmail.com Cc: mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2 1/1] sched/fair:Reduce unnecessary check preempt in the sched tick Message-ID: References: <20210414022229.5469-1-qianjun.kernel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210414022229.5469-1-qianjun.kernel@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 14, 2021 at 10:22:29AM +0800, qianjun.kernel@gmail.com wrote: > From: jun qian > > As you are already set the TIF_NEED_RESCHED, there is no need > to check resched again. Still no justification; does this actually help anything? > Signed-off-by: jun qian > --- > kernel/sched/fair.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 794c2cb945f8..1a69b5fffe4a 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4360,19 +4360,26 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr) > { > unsigned long ideal_runtime, delta_exec; > struct sched_entity *se; > + struct rq *rq = rq_of(cfs_rq); > s64 delta; > > ideal_runtime = sched_slice(cfs_rq, curr); > delta_exec = curr->sum_exec_runtime - curr->prev_sum_exec_runtime; > if (delta_exec > ideal_runtime) { > - resched_curr(rq_of(cfs_rq)); > + if (!test_tsk_need_resched(rq->curr)) > + resched_curr(rq_of(cfs_rq)); > /* > * The current task ran long enough, ensure it doesn't get > * re-elected due to buddy favours. > */ > clear_buddies(cfs_rq, curr); > return; > - } > + /* > + * If here with TIF_NEED_RESCHED already set from the early entity_tick, > + * there is no need to check again. > + */ > + } else if (test_tsk_need_resched(rq->curr)) > + return; This is horrific style. And, afaict, completely unnecessary.