linux-kernel - Re: [PATCH 0/2] cfq-iosched: fixing RQ

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Date:	Wed, 7 Jul 2010 19:39:49 +0200
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 0/2] cfq-iosched: fixing RQ_NOIDLE handling.

On Wed, Jul 7, 2010 at 7:03 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
> Corrado Zoccolo <czoccolo@...il.com> writes:
>
>> Hi Jens,
>> patch 8e55063 "cfq-iosched: fix corner cases in idling logic", is
>> suspected for some regressions on high end hardware.
>> The two patches from this series:
>> - [PATCH 1/2] cfq-iosched: fix tree-wide handling of rq_noidle
>> - [PATCH 2/2] cfq-iosched: RQ_NOIDLE enabled for SYNC_WORKLOAD
>> fix two issues that I have identified, related to how RQ_NOIDLE is
>> used by the upper layers.
>> First patch makes sure that a RQ_NOIDLE coming after a sequence of
>> possibly idling requests from the same queue on the no-idle tree will
>> clear the noidle_tree_requires_idle flag.
>> Second patch enables RQ_NOIDLE for queues in the idling tree,
>> restoring the behaviour pre-8e55063 patch.
>
> Hi, Corrado,
>
> I ran your kernel through my tests.  Here are the results, up against
> vanilla, deadline, and the blk_yield patch set:
>
Hi Jeff,
can you also add cfq with 8e55063 reverted to the testing mix?

>                 just    just
>                fs_mark  fio        mixed
> -------------------------------+--------------
> deadline        529.44   151.4 | 450.0    78.2
> vanilla cfq     107.88   164.4 |   6.6   137.2
> blk_yield cfq   530.82   158.7 | 113.2    78.6
> corrado cfq      80.82   138.1 |   4.5   130.7

So it doesn't seem to help. I wonder if other parts of that commit are
affecting those workloads.

>
> fs_mark results are in files/second, fio results are in MB/s.  All
> results are the average of 5 runs.  In order to get results for the
> mixed workload for both vanilla and Corrado's kernels, I had to extend
> the runtime from 30s to 300s.
>
> So, the changes proposed in this thread actually make performance worse
> across the board.
>
> I re-ran my tests against a RHEL 5 kernel (which is based on 2.6.18),
> and it shows that fs_mark performance is much better than stock CFQ in
> 2.6.35-rc3, and the mixed workload results are much the same as they are
> now (which is to say, the fs_mark process is completely starved by the
> sequential reader).  So, that problem has existed for a long time.
>
> I'm still in the process of collecting data from production servers and
> will report back with my findings there.

Thanks,
Corrado

>
> Cheers,
> Jeff
>



-- 
__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@...il.com
PhD - Department of Computer Science - University of Pisa, Italy
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