From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9AE982B9B7 for ; Wed, 17 Dec 2025 16:16:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765988167; cv=none; b=EkT4AQAcK9UgtPmjZFeT3qkyk+5rmMOTTxLifhLLYPZ96UMNoMYyuzb6R71OeGptrxcKbdskg6veztW+aApY6aKn7MTqb1PebHDFpTr5o+kvuDXDTtuoV9CaMdHK5LtTv/nhU1S4Yobl2EkI9J0n3UFszEczhMab7mrn4KZ0T5Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765988167; c=relaxed/simple; bh=DYlnpRkFkxpeF8z4jmB8n0S+AeuecJN123Higou7rtg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZqnUmCVX8xcsMBVPKI9ao8LFTfFRjxKUJ/wYUJzRG/QLYUnNg8VN5CdwMs8hJOj0Wda3atT14qVKvlHt0NapMCPqEGTiOIHY6LCsWaa2nGUDbUk7s4cEueJUeit39xO3XgaL3RSN245i/2lZoa3PKo88kTSl4G7eUgdDbYmgS2k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B2A21FEC; Wed, 17 Dec 2025 08:15:56 -0800 (PST) Received: from [10.57.10.168] (unknown [10.57.10.168]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5AE1C3F5CA; Wed, 17 Dec 2025 08:16:01 -0800 (PST) Message-ID: Date: Wed, 17 Dec 2025 17:15:59 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 2/2] sched: update the rq->avg_idle when a task is moved to an idle CPU To: Shijie Huang , Huang Shijie , mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org Cc: patches@amperecomputing.com, cl@linux.com, Shubhang@os.amperecomputing.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, linux-kernel@vger.kernel.org, vschneid@redhat.com, vineethr@linux.ibm.com, kprateek.nayak@amd.com References: <20251209094508.570049-1-shijie@os.amperecomputing.com> <20251209094508.570049-3-shijie@os.amperecomputing.com> <51a9e1c4-3061-488c-89f4-ed656f3a73e3@amperemail.onmicrosoft.com> <0486368b-9cc9-48f3-8074-b72c76aab7e1@arm.com> <99c18623-4533-4dde-a765-ea43c85ee02f@amperemail.onmicrosoft.com> Content-Language: en-GB From: Dietmar Eggemann In-Reply-To: <99c18623-4533-4dde-a765-ea43c85ee02f@amperemail.onmicrosoft.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 15.12.25 10:35, Shijie Huang wrote: > > On 12/12/2025 22:22, Dietmar Eggemann wrote: >>>> So you could move (1) back to (2) avoiding the 'if rq->idle_stamp' for >>>> the sched_change pattern for instance? >>> Could you please tell me what is "avoiding the 'if rq->idle_stamp' for >>> the sched_change pattern" ? >>> >>> Sorry, I do not understand your meaning. >> sched_change uses dequeue_task()/enqueue_task() for a queued task to >> change prio, policy, sched params, taskgroups, etc. > > For sched_change, the dequeue_task()/enqueue_task() only work when > > the queued task has TASK_ON_RQ_QUEUED flags. The TASK_ON_RQ_QUEUED > > is set in activate_task(). I guess this was a misunderstanding. It works because of 'if (rq->idle_stamp)' and setting 'rq->idle_stamp = 0' within the condition but this condition isn't worth checking in certain places where we actually call enqueue_task(). > >   1.) For this active task, if the sched_change makes it dequeue_task()/ > enqueue_task() on > >       current CPU, it's okay. Since current CPU is not in the newidle, > the "rq->idle_stamp" is 0 at this case. > >       This patch works fine. > > >  2.) For this active task, if the sched_change makes it dequeue_task()/ > enqueue_task() on an another CPU, > >       it's okay too. > >          2.1) If the another CPU's idle_stamp is 0, the another CPU is > busy now. > >                  The sched_change works fine with this patch. > >          2.2) If the another CPU's idle_stamp is not 0, the sched_change > also works fine with this patch. > >                 Since the sched_change is breaking the idle state of the > another CPU by moving an active > >                 task to an idle CPU. It makes sense. Not sure about this. I thought so far that the sched_change pattern is doing a task dequeue + enqueue on the same CPU (this CPU or other)? So you can't come out of idle here. We lock the rq before we call scoped_guard (sched_change, ...) I think Vincent is right by saying the update_rq_avg_idle() should be put into put_prev_task_idle() instead. Still waiting for the DCPerf Mediawiki test results to see if this change fixes my 'rq->avg_idle being too big' issue.