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Date: Sun, 22 Jun 2008 12:41:48 -0700 (PDT)
From: Eric Rannaud <eric.rannaud@gmail.com>
To: Andrea Righi <righi.andrea@gmail.com>
cc: Divyesh Shah <dpshah@google.com>, balbir@linux.vnet.ibm.com,
       menage@google.com, linux-kernel@vger.kernel.org, axboe@kernel.dk,
       matt@bluehost.com, roberto@unbit.it, randy.dunlap@oracle.com,
       akpm@linux-foundation.org
Subject: Re: i/o bandwidth controller infrastructure
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References: <20030410181011$6d15@gated-at.bofh.it> <aC1Yl-2AL-1@gated-at.bofh.it> <75b07c02-1595-4af2-ac87-3b067459f62e@w8g2000prd.googlegroups.com> <48D0786A-AC3B-46C3-B35C-EAAA47BFAEBC@google.com> <4856EB9D.6070804@gmail.com>
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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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