linux-kernel - Re: [RFC v2] sched/rt: Fix RT (group) throttling with nohz

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Date:   Mon, 22 Feb 2021 14:44:46 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Jonathan Schwender <schwenderjonathan@...il.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org
Subject: Re: [RFC v2] sched/rt: Fix RT (group) throttling with nohz_full

On 2021-02-02 10:00:10 [+0100], Jonathan Schwender wrote:
> If nohz_full is enabled (more precisely HK_FLAG_TIMER is set), then
> do_sched_rt_period_timer may be called on a housekeeping CPU,
> which would not service the isolated CPU for a non-root cgroup
> (requires a kernel with RT_GROUP_SCHEDULING).
> This causes RT tasks in a non-root cgroup to get throttled
> indefinitely (unless throttling is disabled) once the timer has
> been moved to a housekeeping CPU.
> To fix this, housekeeping CPUs now service all online CPUs
> if HK_FLAG_TIMER (nohz_full) is set.

This originates from
   https://lore.kernel.org/linux-rt-users/b07b6fc7-1a5f-0dcc-ca65-821de96cd8b4@gmail.com/

Could someone please take a look?

Sebastian