linux-kernel - Re: [PATCH v2 00/10] Add kernel cmdline option for rt_group

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Message-ID: <20250401110508.GH25239@noisy.programming.kicks-ass.net>
Date: Tue, 1 Apr 2025 13:05:08 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Michal Koutný <mkoutny@...e.com>
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Frederic Weisbecker <fweisbecker@...e.com>
Subject: Re: [PATCH v2 00/10] Add kernel cmdline option for rt_group_sched

On Mon, Mar 10, 2025 at 06:04:32PM +0100, Michal Koutný wrote:
> Despite RT_GROUP_SCHED is only available on cgroup v1, there are still
> some (v1-bound) users of this feature. General purpose distros (e.g.
> [1][2][3][4]) cannot enable CONFIG_RT_GROUP_SCHED easily:
> - since it prevents creation of RT tasks unless RT runtime is determined
>   and distributed into cgroup tree,
> - grouping of RT threads is not what is desired by default on such
>   systems,
> - it prevents use of cgroup v2 with RT tasks.
> 
> This changeset aims at deferring the decision whether to have
> CONFIG_RT_GROUP_SCHED or not up until the boot time.
> By default RT groups are available as originally but the user can
> pass rt_group_sched=0 kernel cmdline parameter that disables the
> grouping and behavior is like with !CONFIG_RT_GROUP_SCHED (with certain
> runtime overhead).
> 
> The series is organized as follows:

Right, so at OSPM we had a proposal for a cgroup-v2 variant of all this
that's based on deadline servers. And I am hoping we can eventually
either fully deprecate the v1 thing or re-implement it sufficiently
close without breaking the interface.

But this is purely about enabling cgroup-v1 usage, right?

You meantion some overhead of having this on, is that measured and in
the patches?

Anyway, I'll go have a peek now, finally :-)