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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD4F1C43334 for ; Wed, 20 Jul 2022 12:50:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241085AbiGTMuu (ORCPT ); Wed, 20 Jul 2022 08:50:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52998 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240604AbiGTMum (ORCPT ); Wed, 20 Jul 2022 08:50:42 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 792672A70B for ; Wed, 20 Jul 2022 05:50:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=P7OGlEo0f4NPfbw6CNnrOlcfGnGBeVJ5/cXY1HeGBK4=; b=W6fRInLWvmypStI1rDrhN/4aaX qO7u5h9DX5l7jO9sIL9pQoTfpottHTtkudzpIKt76TZA58R/3PDePSgHcleCSdFu9WIS10Vdk5Q6m 0hjJBUipyrsqpHcEuYpkiNotSknGbfofDkuzGHrV1T9x1TAUCGbhUUQRyG+hORJ5raONC0fkKxE2g MFoMZFoQ0zfgCSnj95jFcsUNX4sCHFrQygvPErC34xURjSjCrzOIRmtqUEM9ks+8rHdyBqn9XmG4O WBJ3xe8xU+W8Tf+FWYEvLf3tg1CtUMYK1+LRsrrbQwzlGkMHK2J6mjk0FTbzZxqemtEPHuRDYoQJM O/V6ljXQ==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=worktop.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1oE99d-005K9M-8U; Wed, 20 Jul 2022 12:50:17 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 7A9DA980BBE; Wed, 20 Jul 2022 14:50:15 +0200 (CEST) Date: Wed, 20 Jul 2022 14:50:15 +0200 From: Peter Zijlstra To: Nicolas Saenz Julienne Cc: linux-kernel@vger.kernel.org, fweisbec@gmail.com, bristot@redhat.com, vschneid@redhat.com, cmetcalf@ezchip.com, mgorman@suse.de, bsegall@google.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, vincent.guittot@linaro.org, juri.lelli@redhat.com, mingo@redhat.com, mtosatti@redhat.com Subject: Re: [PATCH] nohz/full, sched/rt: Fix missed tick-reenabling bug in dequeue_task_rt Message-ID: References: <20220628092259.330171-1-nsaenzju@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 13, 2022 at 07:18:42PM +0200, Nicolas Saenz Julienne wrote: > On Tue, 2022-06-28 at 11:22 +0200, Nicolas Saenz Julienne wrote: > > dequeue_task_rt() only decrements 'rt_rq->rt_nr_running' after having > > called sched_update_tick_dependency() preventing it from re-enabling the > > tick on systems that no longer have pending SCHED_RT tasks but have > > multiple runnable SCHED_OTHER tasks: > > > > dequeue_task_rt() > > dequeue_rt_entity() > > dequeue_rt_stack() > > dequeue_top_rt_rq() > > sub_nr_running() // decrements rq->nr_running > > sched_update_tick_dependency() > > sched_can_stop_tick() // checks rq->rt.rt_nr_running, > > ... > > __dequeue_rt_entity() > > dec_rt_tasks() // decrements rq->rt.rt_nr_running > > ... > > > > Every other scheduler class performs the operation in the opposite > > order, and sched_update_tick_dependency() expects the values to be > > updated as such. So avoid the misbehaviour by inverting the order in > > which the above operations are performed in the RT scheduler. > > > > Fixes: 76d92ac305f2 ("sched: Migrate sched to use new tick dependency mask model") > > Signed-off-by: Nicolas Saenz Julienne > > --- > > Ping :) Thanks! got stuck in the retbleed backlog :/