linux-kernel - Re: [PATCH] AIO: Don't plug the I/O queue in do_io

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Message-ID: <x49sjkoi08u.fsf@segfault.boston.devel.redhat.com>
Date:	Tue, 13 Dec 2011 17:18:41 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Dave Kleikamp <dave.kleikamp@...cle.com>
Cc:	linux-aio@...ck.org, linux-kernel@...r.kernel.org,
	Chris Mason <chris.mason@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] AIO: Don't plug the I/O queue in do_io_submit()

Dave Kleikamp <dave.kleikamp@...cle.com> writes:

> Asynchronous I/O latency to a solid-state disk greatly increased
> between the 2.6.32 and 3.0 kernels. By removing the plug from
> do_io_submit(), we observed a 34% improvement in the I/O latency.
>
> Unfortunately, at this level, we don't know if the request is to
> a rotating disk or not.

I'm guessing I know the answer to this, but what workload were you
testing, and can you provide more concrete evidence than "latency
greatly increased?"  Also, have you tested the effects this has when
using traditional storage for whatever your workload is?  I don't feel
comfortable essentially reverting a performance patch without knowing
the entire picture.  I will certainly do some testing on my end, too.

Cheers,
Jeff
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