linux-kernel - Re: [PATCH] cfq-iosched: reduce write depth only if sync was delayed

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Date:	Fri, 11 Dec 2009 18:15:20 +0100
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH] cfq-iosched: reduce write depth only if sync was delayed

Hi Jeff,
On Wed, Dec 9, 2009 at 7:09 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
> Corrado Zoccolo <czoccolo@...il.com> writes:
>
>> The numbers look good. Now, there is no penalty in having low_latency
>> set for sequential writes, and just a small penalty for random ones.
>> The fact that random reads are faster with low_latency set is interesting.
>> Is the test is running with your patched tiobench (so that the number
>> of random operations is comparable with sequential ones)?
>
> No, I forgot all about that.  The number of random operations defaults
> to 4000, which is pretty low.  I'll re-run the tests with a number
> comparable to the sequential runs.  Sorry about that.
>
N.P.
if you have time, can you also re-run the test changing:
iosched/fifo_expire_async to 8 ?
I hope that reducing the expire_async, will make cfq quicker at switching
between the different threads, allowing more parallelism for seq
writers on your hw.
If this is the case, I think I can try to estimate the
fifo_expire_async in the autotuning patch.

> Cheers,
> Jeff
>

Thanks
Corrado
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