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From: Jens Axboe <[email protected]>
To: Felix Moessbauer <[email protected]>, [email protected]
Cc: [email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected]
Subject: Re: [PATCH 1/1] io_uring/sqpoll: inherit cpumask of creating process
Date: Fri, 6 Sep 2024 07:47:24 -0600	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

On 9/6/24 7:44 AM, Felix Moessbauer wrote:
> The submit queue polling threads are "kernel" threads that are started

It's not a kernel thread, it's a normal userland thread that just never
exits to userspace.

> from the userland. In case the userland task is part of a cgroup with
> the cpuset controller enabled, the poller should also stay within that
> cpuset. This also holds, as the poller belongs to the same cgroup as
> the task that started it.
> 
> With the current implementation, a process can "break out" of the
> defined cpuset by creating sq pollers consuming CPU time on other CPUs,
> which is especially problematic for realtime applications.
> 
> Part of this problem was fixed in a5fc1441 by dropping the
> PF_NO_SETAFFINITY flag, but this only becomes effective after the first
> modification of the cpuset (i.e. the pollers cpuset is correct after the
> first update of the enclosing cgroups cpuset).
> 
> By inheriting the cpuset of the creating tasks, we ensure that the
> poller is created with a cpumask that is a subset of the cgroups mask.
> Inheriting the creators cpumask is reasonable, as other userland tasks
> also inherit the mask.

Looks fine to me.

-- 
Jens Axboe



  reply	other threads:[~2024-09-06 13:47 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-09-06 13:44 [PATCH 1/1] io_uring/sqpoll: inherit cpumask of creating process Felix Moessbauer
2024-09-06 13:47 ` Jens Axboe [this message]
2024-09-06 13:52   ` MOESSBAUER, Felix
2024-09-06 13:55     ` Jens Axboe
2024-09-06 13:54 ` Jens Axboe
2024-09-06 16:00 ` Jens Axboe

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