linux-kernel - Re: [RFC PATCH v4 15/28] sched/rt: Allow zeroing the runtime of the root control group

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aXCrTNd2M0rnj9NA@jlelli-thinkpadt14gen4.remote.csb>
Date: Wed, 21 Jan 2026 11:32:44 +0100
From: Juri Lelli <juri.lelli@...hat.com>
To: Yuri Andriaccio <yurand2000@...il.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	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>,
	linux-kernel@...r.kernel.org,
	Luca Abeni <luca.abeni@...tannapisa.it>,
	Yuri Andriaccio <yuri.andriaccio@...tannapisa.it>
Subject: Re: [RFC PATCH v4 15/28] sched/rt: Allow zeroing the runtime of the
 root control group

Hello,

On 01/12/25 13:41, Yuri Andriaccio wrote:
> In HCBS, the root control group follows the already existing rules for
> rt-task scheduling. As such, it does not make use of the deadline servers
> to account for runtime, or any other HCBS specific code and features.
> 
> While the runtime of SCHED_DEADLINE tasks depends on the global bandwidth
> reserved for rt_tasks, the runtime of SCHED_FIFO/SCHED_RR tasks is limited
> by the activation of fair-servers (as the RT_THROTTLING mechanism has been
> removed in favour of them), thus their maximum bandwidth depends solely on
> the fair-server settings (which are thightly related to the global
> bandwidth reserved for rt-tasks) and the amount of SCHED_OTHER workload to
> run (recall that if no SCHED_OTHER tasks are running, the FIFO/RR tasks
> may fully utilize the CPU).
> 
> The values of runtime and period in the root cgroup's cpu controller do
> not affect, by design of HCBS, the fair-server settings and similar
> (consequently they do not affect the scheduling of FIFO/RR tasks in the
> root cgroup), but they are just used to reserve a portion of the
> SCHED_DEADLINE bandwidth to the scheduling of rt-cgroups. These values
> only affect child cgroups, their deadline servers and their assigned
> FIFO/RR tasks.
> 
> Signed-off-by: Yuri Andriaccio <yurand2000@...il.com>

Reviewed-by: Juri Lelli <juri.lelli@...hat.com>

Thanks,
Juri