linux-kernel - Re: [patch,rfc] cfq: merge cooperating cfq

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Message-ID: <x4963a2yz3a.fsf@segfault.boston.devel.redhat.com>
Date:	Mon, 26 Oct 2009 11:06:01 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	jens.axboe@...cle.com,
	Linux Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: [patch,rfc] cfq: merge cooperating cfq_queues

Corrado Zoccolo <czoccolo@...il.com> writes:

> Hi
> On Thu, Oct 22, 2009 at 2:09 AM, Jeff Moyer <jmoyer@...hat.com> wrote:
>> I think it's wrong to call the userspace programs broken.  They worked
>> fine when CFQ was quantum based, and they work well with noop and
>> deadline.
>
> So they didn't work well with anticipatory, that was the default from
> 2.6.0 to 2.6.17, and with CFQ with time slices, that was the default
> from 2.6.18 up to now.  I think enough time has passed to start fixing
> those programs.

I actually didn't test anticipatory, so I'm not sure about that one.

> I think fixing nfsd at least for TCP should be easy. In TCP case, each
> client has a private thread pool, so you can just share the I/O
> context once, when creating those threads, and forget it.

I don't think it's a thread pool per client.  Where did you get that
impression?  Simply changing nfsd to use a single I/O context may be an
approachable solution to the problem.  I'm not sure if it's optimal, but
it has to be better than what we have today.

> For the UDP case, would just reducing idle window fix the problem? Or
> the problem is not really the idling, but the bad I/O pattern?

I think the two cases can be handled the same way.  I'll look into it if
time permits.

Cheers,
Jeff
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