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

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Message-ID: <x49zk1rvxm2.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 06 Dec 2012 13:33:57 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jens Axboe <jaxboe@...ionio.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm\@kvack.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

Tejun Heo <tj@...nel.org> writes:

> 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.

I'm in favor of a more general approach.  For now, I'm still going to
push a patch that at least binds to the proper numa node.  I'll post
that after I've tested it.

Cheers,
Jeff
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