linux-kernel - Re: i/o bandwidth controller infrastructure

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Message-ID: <alpine.LFD.1.10.0806221232070.2247@localhost.localdomain>
Date:	Sun, 22 Jun 2008 12:41:48 -0700 (PDT)
From:	Eric Rannaud <eric.rannaud@...il.com>
To:	Andrea Righi <righi.andrea@...il.com>
cc:	Divyesh Shah <dpshah@...gle.com>, balbir@...ux.vnet.ibm.com,
	menage@...gle.com, linux-kernel@...r.kernel.org, axboe@...nel.dk,
	matt@...ehost.com, roberto@...it.it, randy.dunlap@...cle.com,
	akpm@...ux-foundation.org
Subject: Re: i/o bandwidth controller infrastructure

On Tue, 17 Jun 2008, Andrea Righi wrote:
> > With this bandwidth controller, a cpu-intensive job which otherwise  does
> > not care about its IO
> > performance needs to be pin-point accurate about IO bandwidth  required in
> > order to not suffer
> > from cpu-throttling. IMHO, if a cgroup is exceeding its limit for a  given
> > resource, the throttling
> > should be done _only_ for that resource.
> 
> I understand your point of view. It would be nice if we could just
> "disable" the i/o for a cgroup that exceeds its limit, instead of
> scheduling some sleep()s, so the tasks running in this cgroup would be
> able to continue their non-i/o operations as usual.
> 
> However, how to do if the tasks continue to perform i/o ops under this
> condition? we could just cache the i/o in memory and at the same time
> reduce the i/o priority of those tasks' requests, but this would require
> a lot of memory, more space in the page cache, and probably could lead
> to potential OOM conditions. A safer approach IMHO is to force the tasks
> to wait synchronously on each operation that directly or indirectly
> generates i/o. The last one is the solution implemented by this
> bandwidth controller.

What about AIO? Is this approach going to make the task sleep as well?
Would it better to return from aio_write()/_read() with EAGAIN?

Thanks.
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