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 44D7BC433EF for ; Fri, 1 Jul 2022 11:25:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235224AbiGALZl (ORCPT ); Fri, 1 Jul 2022 07:25:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54890 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231781AbiGALZe (ORCPT ); Fri, 1 Jul 2022 07:25:34 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 872847B34B for ; Fri, 1 Jul 2022 04:25:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1656674732; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=5OmlA/t9RccN7KSRkjLQlSW9pQ8XucLvZm0GyPWgBPo=; b=fDw/8ApdxWwGk/KpKDJW5O3er5VSsD8SxjF2g+NaduXzpU07+O6oR+cIUPNerQeTv0VzMd RWeGBOmZ1eE5eSS5j7bCVJA+dE+NO4A/QS8qn4iI5AFC3XvEJFaHsUmJ2EzP9phw09Mbmv T2cYsjuzbnXTlUGuKpRp3aMFH0l9oCo= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-669-034TTLxxOD2edDV_xLTQGQ-1; Fri, 01 Jul 2022 07:25:31 -0400 X-MC-Unique: 034TTLxxOD2edDV_xLTQGQ-1 Received: by mail-wm1-f70.google.com with SMTP id j35-20020a05600c1c2300b003a167dfa0ecso1268567wms.5 for ; Fri, 01 Jul 2022 04:25:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=5OmlA/t9RccN7KSRkjLQlSW9pQ8XucLvZm0GyPWgBPo=; b=uf91WdYe9Zy73juyyr7821l8+7/UogScb3w5cRSEMqQy/rWdjl1x9TO7w7tMxUVUdS qVTuHpH77qAVG1FMKhqXgTRchw7cagv2eDN8Zi5od2dKc1Bm82InlHClCCMKVJ7w84gX UzXng19mCma1GRKgSBFXYYP2TBcUb9aEkpi9unfJcbedw8ppzqdcpHJHaDx5wcEFLZ9A +KSpCYcu0u3AzFa/0f8eNCr9cclxCsw45qJahjxWsyCSJ4QCYAHjU0xeY1+PJtWTk5TB tI0MzN0xpDTUgoZ9cus/PiGyp7cmo0VMlUyZQLqovo8lKEmAblWCjgObFX3HLksuX3S0 QjiA== X-Gm-Message-State: AJIora8717vGJsKSsMOLKJ7djZ62216/KfmU1ywwUMSUqzM55jJV3uHf QAj+mx4StieaCxF4pLNvqXgHbBTbZyygja3zdHnTHhgDZ5pGyX4LtNRGjotl+vkn7OT6qiejIUp MAXCOrFNbwWloD6NzqE7gfKJ3 X-Received: by 2002:a1c:720f:0:b0:3a0:2ac9:5231 with SMTP id n15-20020a1c720f000000b003a02ac95231mr15818998wmc.39.1656674730549; Fri, 01 Jul 2022 04:25:30 -0700 (PDT) X-Google-Smtp-Source: AGRyM1v/lwU2oxUG3naM8CeuP8DCWGu05RJ3M2eBqVXS9RJaaGCh4Va3ISeKKIPp16rjvj7DLxzF0w== X-Received: by 2002:a1c:720f:0:b0:3a0:2ac9:5231 with SMTP id n15-20020a1c720f000000b003a02ac95231mr15818981wmc.39.1656674730362; Fri, 01 Jul 2022 04:25:30 -0700 (PDT) Received: from vschneid.remote.csb ([185.11.37.247]) by smtp.gmail.com with ESMTPSA id w6-20020a5d4b46000000b0021d3fbf1d29sm3862405wrs.97.2022.07.01.04.25.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 Jul 2022 04:25:29 -0700 (PDT) From: Valentin Schneider To: Nicolas Saenz Julienne , linux-kernel@vger.kernel.org, fweisbec@gmail.com Cc: bristot@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, peterz@infradead.org, mingo@redhat.com, mtosatti@redhat.com, Nicolas Saenz Julienne Subject: Re: [PATCH] nohz/full, sched/rt: Fix missed tick-reenabling bug in dequeue_task_rt In-Reply-To: <20220628092259.330171-1-nsaenzju@redhat.com> References: <20220628092259.330171-1-nsaenzju@redhat.com> Date: Fri, 01 Jul 2022 12:25:28 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/06/22 11:22, 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. > I can't see anything wrong with your approach, though I did have to spend some time re-learning RT_GROUP_SCHED. The designated Fixes: commit looks about right too. > Fixes: 76d92ac305f2 ("sched: Migrate sched to use new tick dependency mask model") > Signed-off-by: Nicolas Saenz Julienne Reviewed-by: Valentin Schneider