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 C19291EA80; Tue, 6 Feb 2024 12:56:26 +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=1707224186; cv=none; b=GzVo1K0iVv54zGtDjqSKzxdAFZwqyNkxldwK0RE1YDIR1JOpFQFbZA+mCrraHDWRe0UZ9SIabs2JuBsvVuU/XEgOWxMgy4EItez7L1wC3KYkgI1+oS+TOf6keJLQZ+ipWubDAnlx/W11tMY4rpCDtZVtp29tUasfHrf/S/j8Ht8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707224186; c=relaxed/simple; bh=hPZSu02P2dfzA6Y4MG5ytfc6LxdzfYU+fY/Tl4zL5jM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ChF9qjuesjM228xt51lKSYWh8/RLnxv3rUyG2u5ERKqcv+V+CEc9FJwllXNb8MMMmmbX9C4gUVL78X1jf8/5CC7SSd+Ovse6Wj2GcTjy+ND8/ju024xi71BK7+6H7TzhfnmSBZdVCOQqrAtP8+v9xv9hNU9vu5TMQ96qVKhD5ME= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cefG3SlK; 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="cefG3SlK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B5FBBC433F1; Tue, 6 Feb 2024 12:56:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1707224186; bh=hPZSu02P2dfzA6Y4MG5ytfc6LxdzfYU+fY/Tl4zL5jM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=cefG3SlKw+inRWFc3vcRQS1w3RgS3nyUQpf4AcH3AIpRY+RrehgF9qN2E3TxAOwIN mBelaXz3vxZGk+ksUPseP9Tnq4XQBmED9DFuwn9vir+UJsYXW3V5XlQ7ko66nRR0AF H4gfnUlHYTzz6FLQqGiHeoT6zTkPPtq/g6RDneyM07t4DVULZoitFY1xq2KXAaFHJC UOs/OYm5FGKGD3xZEm4/FMz+/8v4uF6fWQ3gbTaTa5OSFRGojFpNlUXm9TQLkkC8rs /oMAkGl1yArPwXD4UUZCjh6AL5WVM2y0OJBnvZAU2wmnVK0U65lsb3ztL957APWAk9 2Wol22Eiq73xQ== Date: Tue, 6 Feb 2024 13:56:23 +0100 From: Frederic Weisbecker To: Waiman Long Cc: 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 , Marcelo Tosatti , 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: <5ee5bf79-6cdc-4d1b-a19f-f0d5165a5f16@redhat.com> 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... 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.