linux-kernel - Re: [patch,v2] bdi: add a user-tunable cpu

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Message-ID: <20121206182239.GS19802@htj.dyndns.org>
Date:	Thu, 6 Dec 2012 10:22:39 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	Jeff Moyer <jmoyer@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Zach Brown <zab@...hat.com>,
	Peter Zijlstra <pzijlstr@...hat.com>, Ingo <mingo@...hat.com>
Subject: Re: [patch,v2] bdi: add a user-tunable cpu_list for the bdi flusher
 threads

Hello, Jens.

On Thu, Dec 06, 2012 at 07:19:34PM +0100, Jens Axboe wrote:
> We need to expose it. Once the binding is set from the kernel side on a
> kernel thread, it can't be modified.

That's only if kthread_bind() is used.  Caling set_cpus_allowed_ptr()
doesn't set PF_THREAD_BOUND and userland can adjust affinity like any
other tasks.

> Binding either for performance reasons or for ensuring that we
> explicitly don't run in some places is a very useful feature.

Sure, but I think this is too specific.  Something more generic would
be much better.  It can be as simple as generating a uevent.

Thanks.

-- 
tejun
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