From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 B2C127D3E6; Wed, 7 Feb 2024 14:47:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707317269; cv=none; b=t/AfrvzZKvEJfMvQ0/MXJLmniPCW0FUVaTQbLtFq1SPiwdPoV6FGdMX+FKiKKTJKWryV8X8VIvXqYKv5OCpufvwziFz4o5FwpPlohjp2uH9HKcqUvnpvZ8M9q2whbqJiZy09a0N+VdbkQrzaGGVYsP50ed7zDVTvOsxIDPM2kzQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707317269; c=relaxed/simple; bh=dqeS7RKaqg5NSBHC9tqAZ0jlOtvjCCV80N050qidhz4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=HzRYVwZOikh7PXvTpnuv/06Xu2fFITQA/EscgbNhWI5kfxylcErZiV/1PxlIryufU3rJnoZvIAr4aIQmDhl6b/8pnBpQ2Z2cFm4wPcMxSxIvyU36uZIu6wu/4mG4wKQDKvVQMT+A4rIm0lvfKnBhZYek5fsNYsl7TkK7K6SNJmc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=icYajaCA; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="icYajaCA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B241DC433C7; Wed, 7 Feb 2024 14:47:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1707317269; bh=dqeS7RKaqg5NSBHC9tqAZ0jlOtvjCCV80N050qidhz4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=icYajaCA2tFuTuC9D1SNlZkAipRaQApzHfHrIPO4rCmYFsJxTQhhfFshiqBzaCWju y12CJHYXvQttTjw5qpXSAtyLcfMStuhpTAyRQEhLzToFX0NrTqDP81kOhE2wMFrQpM HQB9k4CEAY9lkMSxxC4tQYBwQ1ilFaMSUNmfR1zqzAlallx3LLJP2zBl/kNfc8/tvz 7y6rbmy/s3mgvrPkcOT9x/RJ0buI/rNL47I4cQaFBkfRU1n/g7tiArc81Jx7KqxO5w ySeNZCGRyg6jIOTOdyZoouhyyFlMC3z9ynle0GLAdzOCw7gKdklno1RqDO4QEusQcT XVhPLhZv65j0w== Date: Wed, 7 Feb 2024 15:47:46 +0100 From: Frederic Weisbecker To: Marcelo Tosatti Cc: Waiman Long , Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet , "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Davidlohr Bueso , Shuah Khan , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-kselftest@vger.kernel.org, Mrunal Patel , Ryan Phillips , Brent Rowsell , Peter Hunt , Cestmir Kalina , Nicolas Saenz Julienne , Alex Gladkov , Phil Auld , Paul Gortmaker , Daniel Bristot de Oliveira , Juri Lelli , Peter Zijlstra , Costa Shulyupin Subject: Re: [RFC PATCH 0/8] cgroup/cpuset: Support RCU_NOCB on isolated partitions Message-ID: References: <20240117163511.88173-1-longman@redhat.com> <5ee5bf79-6cdc-4d1b-a19f-f0d5165a5f16@redhat.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Le Tue, Feb 06, 2024 at 04:15:18PM -0300, Marcelo Tosatti a écrit : > On Tue, Feb 06, 2024 at 01:56:23PM +0100, Frederic Weisbecker wrote: > > Le Wed, Jan 17, 2024 at 12:15:07PM -0500, Waiman Long a écrit : > > > > > > On 1/17/24 12:07, Tejun Heo wrote: > > > > Hello, > > > > > > > > On Wed, Jan 17, 2024 at 11:35:03AM -0500, Waiman Long wrote: > > > > > The first 2 patches are adopted from Federic with minor twists to fix > > > > > merge conflicts and compilation issue. The rests are for implementing > > > > > the new cpuset.cpus.isolation_full interface which is essentially a flag > > > > > to globally enable or disable full CPU isolation on isolated partitions. > > > > I think the interface is a bit premature. The cpuset partition feature is > > > > already pretty restrictive and makes it really clear that it's to isolate > > > > the CPUs. I think it'd be better to just enable all the isolation features > > > > by default. If there are valid use cases which can't be served without > > > > disabling some isolation features, we can worry about adding the interface > > > > at that point. > > > > > > My current thought is to make isolated partitions act like isolcpus=domain, > > > additional CPU isolation capabilities are optional and can be turned on > > > using isolation_full. However, I am fine with making all these turned on by > > > default if it is the consensus. > > > > Right it was the consensus last time I tried. Along with the fact that mutating > > this isolation_full set has to be done on offline CPUs to simplify the whole > > picture. > > > > So lemme try to summarize what needs to be done: > > > > 1) An all-isolation feature file (that is, all the HK_TYPE_* things) on/off for > > now. And if it ever proves needed, provide a way later for more finegrained > > tuning. > > > > 2) This file must only apply to offline CPUs because it avoids migrations and > > stuff. > > > > 3) I need to make RCU NOCB tunable only on offline CPUs, which isn't that much > > changes. > > > > 4) HK_TYPE_TIMER: > > * Wrt. timers in general, not much needs to be done, the CPUs are > > offline. But: > > * arch/x86/kvm/x86.c does something weird > > * drivers/char/random.c might need some care > > * watchdog needs to be (de-)activated > > > > 5) HK_TYPE_DOMAIN: > > * This one I fear is not mutable, this is isolcpus... > > Except for HK_TYPE_DOMAIN, i have never seen anyone use any of this > flags. HK_TYPE_DOMAIN is used by isolcpus=domain,.... HK_TYPE_MANAGED_IRQ is used by isolcpus=managed_irq,... All the others (except HK_TYPE_SCHED) are used by nohz_full= Thanks. > > > > > 6) HK_TYPE_MANAGED_IRQ: > > * I prefer not to think about it :-) > > > > 7) HK_TYPE_TICK: > > * Maybe some tiny ticks internals to revisit, I'll check that. > > * There is a remote tick to take into consideration, but again the > > CPUs are offline so it shouldn't be too complicated. > > > > 8) HK_TYPE_WQ: > > * Fortunately we already have all the mutable interface in place. > > But we must make it live nicely with the sysfs workqueue affinity > > files. > > > > 9) HK_FLAG_SCHED: > > * Oops, this one is ignored by nohz_full/isolcpus, isn't it? > > Should be removed? > > > > 10) HK_TYPE_RCU: > > * That's point 3) and also some kthreads to affine, which leads us > > to the following in HK_TYPE_KTHREAD: > > > > 11) HK_FLAG_KTHREAD: > > * I'm guessing it's fine as long as isolation_full is also an > > isolated partition. Then unbound kthreads shouldn't run there. > > > > 12) HK_TYPE_MISC: > > * Should be fine as ILB isn't running on offline CPUs. > > > > Thanks. > > > > >