Re: [PATCH 0/2] cfq-iosched: fixing RQ_NOIDLE handling.

[Jeff Moyer <jmoyer@redhat.com>]

Corrado Zoccolo <czoccolo@gmail.com> writes:

> On Wed, Jul 7, 2010 at 7:03 PM, Jeff Moyer <jmoyer@redhat.com> wrote:
>> Corrado Zoccolo <czoccolo@gmail.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.

It's worth noting that I can't explain that jump from 151MB/s for
deadline vs 220MB/s for corrado cfq.  I'm not sure how you can vary
driving a single queue depth sequential read at all.  Those are the
averages of 5 runs and this storage should be solely accessible by me,
so I am at a loss.

Cheers,
Jeff