linux-kernel - Re: tiobench read 50% regression with 2.6.30-rc1

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Message-ID: <x49skkagm8j.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 15 Apr 2009 08:00:44 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	"Zhang\, Yanmin" <yanmin_zhang@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: tiobench read 50% regression with 2.6.30-rc1

Jens Axboe <jens.axboe@...cle.com> writes:

> On Wed, Apr 15 2009, Jeff Moyer wrote:
>> Jens Axboe <jens.axboe@...cle.com> writes:
>> 
>> > On Wed, Apr 15 2009, Jeff Moyer wrote:
>> >> I tested this using iozone to read a file from an NFS client.  The
>> >> iozone command line was:
>> >>   iozone -s 2000000 -r 64 -f /mnt/test/testfile -i 1 -w
>> >> 
>> >> The numbers in the nfsd's row represent the number of nfsd threads.  I
>> >> included numbers for the deadline scheduler as well for comparison.
>> >> 
>> >>                v2.6.29
>> >> 
>> >> nfsd's  |   1    |  2   |   4   |   8
>> >> --------+---------------+-------+------
>> >> cfq     | 91356 | 66391 | 61942 | 51674
>> >> deadline| 43207 | 67436 | 96289 | 107784
>> >> 
>> >>               2.6.30-rc1
>> >> 
>> >> nfsd's  |   1   |   2   |   4   |   8
>> >> --------+---------------+-------+------
>> >> cfq     | 43127 | 22354 | 20858 | 21179
>> >> deadline| 43732 | 68059 | 76659 | 83231
>> >> 
>> >>           2.6.30-rc1 + cfq fix
>> >> 
>> >> nfsd's  |   1    |    2   |   4   |   8
>> >> --------+-----------------+-------+------
>> >> cfq     | 114602 | 102280 | 43479 | 43160
>> >> 
>> >> As you can see, for 1 and 2 threads, the patch *really* helps out.  We
>> >> still don't get back the performance for 4 and 8 nfsd threads, though.
>> >> It's interesting to note that the deadline scheduler regresses for 4 and
>> >> 8 threads, as well.  I think we've still got some digging to do.
>> >
>> > Wow, that does indeed look pretty good!
>> 
>> Please don't lose the later part of the message, which is that both CFQ
>> and deadline regress for 4 and 8 threads when moving from 2.6.29 to
>> 2.6.30-rc1!  There have been way too many changes to keep track of in
>> this area recently, and I'd like to get some confidence that we
>> understand the performance implications of them.
>
> I'm definitely not, in fact pending patches should make it better! For

OK,  I'll look through the changelog of your for-linus branch.

> the nfs case, I'm still a big proponent of explicitly getting the io
> context sharing in place, instead of adding code at the other end to
> try and fix things up.

OK, I have an ugly patch that wires that up.  I guess it's time to
clean that up and test it.

>> >> I'll try the cfq close cooperator patches next.
>> >
>> > I have a pending update on the coop patch that isn't pushed out yet, I
>> > hope to have it finalized and tested later today. Hopefully, with that,
>> > we should be able to maintain > 100Mb/sec for 4 and 8 threads.
>> 
>> OK, please let me know when and where this is available and I'll give it
>> a try.
>
> I sent you email about ~10 minutes ago or so about that very patch.

Yep, got it.  Thanks!

-Jeff
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