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

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Message-ID: <AANLkTilJFQITg7qK5gKJ9Rwt06KA6fvDr7Ed9u7cbwBX@mail.gmail.com>
Date:	Fri, 9 Jul 2010 21:45:22 +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 Fri, Jul 9, 2010 at 4:07 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
> Corrado Zoccolo <czoccolo@...il.com> writes:
>
>> On Wed, Jul 7, 2010 at 10:06 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
>>> Corrado Zoccolo <czoccolo@...il.com> writes:
>>>
>>>> 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?
>>>
>>> Sure, the results now look like this:
>>>
>>>                 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     110.16   220.6 |   7.0   159.8
>>> 8e55063 revert  559.66   198.9 |  16.1   153.3
>>>
>>> I had accidentally run your patch set (corrado cfq) on ext3, so the
>>> numbers were a bit off (everything else was run against ext4).  The
>>> corrected numbers above reflect the performance on ext4, which is much
>>> better for the sequential reader, but still not great for the fs_mark
>>> run.  Reverting 8e55063 definitely gets us into better shape.  However,
>>> if we care about the mixed workload, then it won't be enough.
>>
>> Wondering why deadline performs so well in the fs_mark workload. Is it
>> because it doesn't distinguish between sync and async writes?
>
> It performs well because it doesn't do any idling.
>
>> Maybe we can achieve something similar by putting all sync writes
>> (that are marked as REQ_NOIDLE) in the noidle tree? This, coupled with
>> making jbd(2) perform sync writes, should make the yield automatic,
>> since they all live in the same tree for which we don't idle between
>> queues, and should be able to provide fairness compared to a
>> sequential reader (that lives in the other tree).
>>
>> Can you test the attached patch, where I also added your changes to
>> make jbd(2) to perform sync writes?
>
> I'm not sure what kernel you generated that patch against.  I'm working
> with 2.6.35-rc3 or later, and your patch does not apply there.
It's Jens' block/for-2.6.36 tree.

>
> Cheers,
> Jeff
>



-- 
__________________________________________________________________________

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