linux-kernel - Re: [RFC PATCH] block: Fix bio merge induced high I/O latency

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Date:	Tue, 20 Jan 2009 23:38:19 -0500
From:	Ben Gamari <bgamari@...il.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Jens Axboe <jens.axboe@...cle.com>
Cc:	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, ltt-dev@...ts.casi.polymtl.ca
Subject: Re: [RFC PATCH] block: Fix bio merge induced high I/O latency

On Tue, Jan 20, 2009 at 7:25 PM, Mathieu Desnoyers
<mathieu.desnoyers@...ymtl.ca> wrote:
> * Mathieu Desnoyers (mathieu.desnoyers@...ymtl.ca) wrote:
>
> As a side-note : I'd like to have my results confirmed by others.

Well, I think the (fixed) patch did help to some degree (I haven't
done fio benchmarks to compare against yet). Unfortunately, the I/O
wait time problem still remains. I have been waiting 3 minutes now for
evolution to start with 88% I/O wait time yet no visible signs of
progress. I've confirmed I'm using the CFQ scheduler, so that's not
the problem.

Also, Jens, I'd just like to point out that the problem is
reproducible across all schedulers. Does your patch seek to tackle a
problem specific to the CFQ scheduler, leaving the I/O wait issue for
later? Just wondering.

I'll post some benchmarks numbers once I have them. Thanks,

- Ben
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