From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Daniel Bristot de Oliveira <daniel@bristot.me>,
Mathias Koehrer <mathias.koehrer@etas.com>
Cc: "linux-rt-users@vger.kernel.org" <linux-rt-users@vger.kernel.org>
Subject: Re: Kernel thread's CPU affinity with isolcpus kernel boot argument
Date: Thu, 25 Feb 2016 17:35:43 +0100 [thread overview]
Message-ID: <56CF2D5F.60306@linutronix.de> (raw)
In-Reply-To: <56CF1A2A.1050203@bristot.me>
On 02/25/2016 04:13 PM, Daniel Bristot de Oliveira wrote:
> On 02/25/2016 11:18 AM, Sebastian Andrzej Siewior wrote:
>> not that I am aware of. There are a few per-CPU threads which have to
>> stay the way they are. I would have expected that others like kworker/u*
>> respect the isol CPUs and stay away.
>
> Isolcpus is applied only for user-space threads. For instance, you
> still need to move rcu offload callbacks away from isolated CPUs, and
> all other kernel threads as well.
RCU is special since this is a per-CPU thread. However Paul did make an
option where you can move those to another CPU.
> In the special case of kworker/u* threads, you need to use a special
> interface to do it. The interface is the following file:
>
> /sys/devices/virtual/workqueue/cpumask
I see it documented in "Documentation/ABI". Oh wait…
> It was implemented on the following commit:
>
> 042f7df workqueue: Allow modifying low level unbound workqueue cpumask
>
> But the default CPU mask is the "cpu_possible_mask".
>
> Sometime ago I sent a patch to modify the default mask of the kworker/u*
> threads, to avoid them on isolated CPUs by default, but it was not
> acked. It was not explicitly nacked, though.
>
> http://www.gossamer-threads.com/lists/linux/kernel/2218495
>
> Should I try it again?
Atleast they do have a default cpumask which you can modify. I don't
see why the kworker should be special here and avoid the isolcpu mask.
I *do* support the default mask being !isolcpus and not cpu_possible.
If you have the time to try again, please do so.
>
> -- Daniel
>
Sebastian
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prev parent reply other threads:[~2016-02-25 16:35 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-15 11:15 Kernel thread's CPU affinity with isolcpus kernel boot argument Mathias Koehrer
2016-02-25 14:18 ` Sebastian Andrzej Siewior
2016-02-25 14:43 ` Josh Cartwright
2016-02-26 10:53 ` Mathias Koehrer
2016-02-25 15:13 ` Daniel Bristot de Oliveira
2016-02-25 16:35 ` Sebastian Andrzej Siewior [this message]
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