From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D354D19259E for ; Thu, 14 Nov 2024 18:44:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731609848; cv=none; b=BCYTpqZZllacSRnjmQ9VI0UPX9EpFBLowdFIGPPmHd4khkND3UsY7p3AQk9xPPLe6emuC0S0EEPCd2mCn93gzTyDo/kylKzX2Qh5g5DqhEzsCTq4sPCMvVr4YhejPGXFU7gwOhnASoc4ncKSA6S61NVzMgV4EP2+Um3RmjfwUnc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731609848; c=relaxed/simple; bh=Q03vjJ5s1nrHoyz+1CUz5PPjOeiFkURMvI6nfkE3ZXU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=AeYBj4cczw5LMZjAES6qtgZozohmaCC7hbkXQJJfjgNeCziMw1jqHOggtmyRuKwt8qjeExjW5JeloWd8ZST7IqZYuF+NK1UL/Y3C08c9yOnquWWVXhvSxHjmsYFB/UdXICcAbctt4EaNWDDrRgUnbXQ3+ZxfCmzMqImC7A5D3b8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=CfVK7uFZ; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="CfVK7uFZ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1731609844; 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=EAeVfk02oDfwwY3n4EGA4ZA9KbhiKvVHyPWkd4Y/Xuw=; b=CfVK7uFZHJ3P9y2mvvplzyv6Wnna5tgvjZYx/90+pbV37D7VXTYQwRKMOvODycGgekENLL KReSHLnZJXv2gYVANoHQkU/n5omeFgkIOioyuuQa3dyrRr0f5VgVfRU1jt+tp1NhjWR/QR g+z8VzdlprNXn75RI9h/Ia5xXDslLNE= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-232-NdgwsRNSNcawzudfg8CLfg-1; Thu, 14 Nov 2024 13:44:02 -0500 X-MC-Unique: NdgwsRNSNcawzudfg8CLfg-1 X-Mimecast-MFC-AGG-ID: NdgwsRNSNcawzudfg8CLfg Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 422EA1954B1E; Thu, 14 Nov 2024 18:43:59 +0000 (UTC) Received: from pauld.westford.csb (unknown [10.22.88.110]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D44653003B71; Thu, 14 Nov 2024 18:43:53 +0000 (UTC) Date: Thu, 14 Nov 2024 13:43:50 -0500 From: Phil Auld To: Juri Lelli Cc: Waiman Long , Tejun Heo , Johannes Weiner , Michal Koutny , Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Qais Yousef , Sebastian Andrzej Siewior , "Joel Fernandes (Google)" , Suleiman Souhlal , Aashish Sharma , Shin Kawamura , Vineeth Remanan Pillai , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [PATCH v2 0/2] Fix DEADLINE bandwidth accounting in root domain changes and hotplug Message-ID: <20241114184350.GE471026@pauld.westford.csb> References: <20241114142810.794657-1-juri.lelli@redhat.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On Thu, Nov 14, 2024 at 04:14:00PM +0000 Juri Lelli wrote: > Thanks Waiman and Phil for the super quick review/test of this v2! > > On 14/11/24 14:28, Juri Lelli wrote: > > ... > > > In all honesty, I still see intermittent issues that seems to however be > > related to the dance we do in sched_cpu_deactivate(), where we first > > turn everything related to a cpu/rq off and revert that if > > cpuset_cpu_inactive() reveals failing DEADLINE checks. But, since these > > seem to be orthogonal to the original discussion we started from, I > > wanted to send this out as an hopefully meaningful update/improvement > > since yesterday. Will continue looking into this. > > About this that I mentioned, it looks like the below cures it (and > hopefully doesn't regress wrt the other 2 patches). > > What do everybody think? > I think that makes sense. I think it's better not to have that deadline call buried the cpuset code as well. Reviewed-by: Phil Auld > --- > Subject: [PATCH] sched/deadline: Check bandwidth overflow earlier for hotplug > > Currently we check for bandwidth overflow potentially due to hotplug > operations at the end of sched_cpu_deactivate(), after the cpu going > offline has already been removed from scheduling, active_mask, etc. > This can create issues for DEADLINE tasks, as there is a substantial > race window between the start of sched_cpu_deactivate() and the moment > we possibly decide to roll-back the operation if dl_bw_deactivate() > returns failure in cpuset_cpu_inactive(). An example is a throttled > task that sees its replenishment timer firing while the cpu it was > previously running on is considered offline, but before > dl_bw_deactivate() had a chance to say no and roll-back happened. > > Fix this by directly calling dl_bw_deactivate() first thing in > sched_cpu_deactivate() and do the required calculation in the former > function considering the cpu passed as an argument as offline already. > > Signed-off-by: Juri Lelli > --- > kernel/sched/core.c | 9 +++++---- > kernel/sched/deadline.c | 12 ++++++++++-- > 2 files changed, 15 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index d1049e784510..43dfb3968eb8 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -8057,10 +8057,6 @@ static void cpuset_cpu_active(void) > static int cpuset_cpu_inactive(unsigned int cpu) > { > if (!cpuhp_tasks_frozen) { > - int ret = dl_bw_deactivate(cpu); > - > - if (ret) > - return ret; > cpuset_update_active_cpus(); > } else { > num_cpus_frozen++; > @@ -8128,6 +8124,11 @@ int sched_cpu_deactivate(unsigned int cpu) > struct rq *rq = cpu_rq(cpu); > int ret; > > + ret = dl_bw_deactivate(cpu); > + > + if (ret) > + return ret; > + > /* > * Remove CPU from nohz.idle_cpus_mask to prevent participating in > * load balancing when not active > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 267ea8bacaf6..6e988d4cd787 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -3505,6 +3505,13 @@ static int dl_bw_manage(enum dl_bw_request req, int cpu, u64 dl_bw) > } > break; > case dl_bw_req_deactivate: > + /* > + * cpu is not off yet, but we need to do the math by > + * considering it off already (i.e., what would happen if we > + * turn cpu off?). > + */ > + cap -= arch_scale_cpu_capacity(cpu); > + > /* > * cpu is going offline and NORMAL tasks will be moved away > * from it. We can thus discount dl_server bandwidth > @@ -3522,9 +3529,10 @@ static int dl_bw_manage(enum dl_bw_request req, int cpu, u64 dl_bw) > if (dl_b->total_bw - fair_server_bw > 0) { > /* > * Leaving at least one CPU for DEADLINE tasks seems a > - * wise thing to do. > + * wise thing to do. As said above, cpu is not offline > + * yet, so account for that. > */ > - if (dl_bw_cpus(cpu)) > + if (dl_bw_cpus(cpu) - 1) > overflow = __dl_overflow(dl_b, cap, fair_server_bw, 0); > else > overflow = 1; > --