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 9313018D636; Wed, 25 Mar 2026 12:46:00 +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=1774442760; cv=none; b=OY9W2Xq0rP9kcAz0B871g5gVzl0vMy295Hl3mEYrRvmQ3uZsrZEhzWZH5u40QGyTvWCljmIqrANvHZRScsaIm87Vj5xlUdByprwzBUaHVxSbTfOrfp191yhybNvxGN4FbJR4vh8vGoC6rBpygn+O9yLYy8l9XGcqDw1swTOCEyg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774442760; c=relaxed/simple; bh=7ttRJXbfw+Yv4qAT4gpjMx4T7NHp7xtdESE4jaBbZxE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=sxTj6qcxn1LbSzldUTvjShs6m5zeUOJZPgBB6Z3oVmekiZG27cRSDL/FsLyCFqqP4nFbhHhuW34i+zuTc0ydfJarWe2+oYiSiCbFvPf+XITdFh2KbCAz3zENW6MAytxe1oxsq5MOm6DeDRLnBp5xeexR7tJjaj9RKQ/kU8j57VE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PG3bMsLh; 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="PG3bMsLh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BEEA9C4CEF7; Wed, 25 Mar 2026 12:45:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774442760; bh=7ttRJXbfw+Yv4qAT4gpjMx4T7NHp7xtdESE4jaBbZxE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PG3bMsLh6HCQxQcKJrfEnzOoZhP82Xjrda7S/eNCVSEBNZvxdm2YZqh2m9sA3CULn XWgljFRwXq8kUexSTlQTO7mKgnQ7jtUBvM57pSozyG6fy2vtqkYwD9oWC2h6SyMJBR PZ5lsIw7hJsDyZpu8mSfoilJOwnvIwoMI0THH8LfvoWFeW47xrJ4rlx/EriraMBJSm I5jT61QOiR70EAG1wmLbuQ3byPymfOHZiFk6Z2EgOBeDCaeHsN2RVHV+piagZQGyH9 y4XG2CdpJ0Uz8OFnEIDW8rQBquMakxznVFPTbX8nX8W2R0T6e5sY7RfHLZKUfClXOQ Wnu7TLF5BDnmQ== Date: Wed, 25 Mar 2026 13:45:57 +0100 From: Frederic Weisbecker To: Sebastian Andrzej Siewior Cc: LKML , Anna-Maria Behnsen , Gabriele Monaco , Ingo Molnar , Jonathan Corbet , Marcelo Tosatti , Marco Crivellari , Michal Hocko , "Paul E . McKenney" , Peter Zijlstra , Phil Auld , Steven Rostedt , Thomas Gleixner , Valentin Schneider , Vlastimil Babka , Waiman Long , linux-doc@vger.kernel.org, John Ogness Subject: Re: [PATCH] doc: Add CPU Isolation documentation Message-ID: References: <20250809094247.8384-1-frederic@kernel.org> <20260320151036.v_Sn93P-@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260320151036.v_Sn93P-@linutronix.de> Le Fri, Mar 20, 2026 at 04:10:36PM +0100, Sebastian Andrzej Siewior a écrit : > On 2025-08-09 11:42:47 [+0200], Frederic Weisbecker wrote: > > --- /dev/null > > +++ b/Documentation/admin-guide/cpu-isolation.rst > > @@ -0,0 +1,338 @@ > You could start with > > .. SPDX-License-Identifier: GPL-2.0 > > at the top. Ok. > > > +============= > > +CPU Isolation > > +============= > … > > +Interface > > +~~~~~~~~~ > > + > > +- :ref:`Documentation/admin-guide/cgroup-v2.rst > + partitions>` > > I've been told by Jonathan once to just use the .rst file without > anything around it and the HTML render will make the link on its own. > > … Hmm, how would that look like? Just this? +- Documentation/admin-guide/cgroup-v2.rst > > > +Tradeoffs > > +~~~~~~~~~ > > + > > +In terms of cost, this is the most invasive isolation feature. It is > > +assumed to be used when the workload spends most of its time in > > +userspace and doesn't rely on the kernel except for preparatory > > +work because: > > + > > +- RCU is slower due to the locked, offloaded and threaded callbacks > > + processing (the same that would be obtained with "rcu_nocb=" boot > > + parameter). > > You mean the callback invocation is delayed? It shouldn't affect grace > period handling and so on. > > … Right. > > > +Checklist > > +========= > > + > > +You have set up each of the above isolation features but you still > > +observe jitters that trash your workload? Make sure to check a few > > +elements before proceeding. > > + > > +Some of these checklist items are similar to those of real time > > +workloads: > > + > > +- Use mlock() to prevent your pages from being swapped away. Page > > + faults are usually not compatible with jitter sensitive workloads. > > + > > +- Avoid SMT to prevent your hardware thread from being "preempted" > > + by another one. > > + > > +- CPU frequency changes may induce subtle sorts of jitter in a > > + workload. Cpufreq should be used and tuned with caution. > > + > > +- Deep C-states may result in latency issues upon wake-up. If this > > + happens to be a problem, C-states can be limited via kernel boot > > + parameters such as processor.max_cstate or intel_idle.max_cstate. > > + > > I intended to make a similar list similar to this for the real time part > but it somehow faded away. There is now the idea to identify kernel > options which are not so optimal which include CPU frequency for > instance. The requirements here are should be the same. We should probably have this to a seperate file that both isolation and rt could link to? Thanks. -- Frederic Weisbecker SUSE Labs