cfq fsync patch testing results (Was: Re: [RFC PATCH] cfq-iosched: IOPS mode for group scheduling and new group_idle tunable)

[Vivek Goyal <vgoyal@redhat.com>]

On Wed, Jul 28, 2010 at 07:57:16PM -0400, Christoph Hellwig wrote:
> On Wed, Jul 28, 2010 at 04:22:12PM -0400, Vivek Goyal wrote:
> > I also did "time firefox &" testing to see how long firefox takes to
> > launch when linus torture test is running and without patch it took
> > around 20 seconds and with patch it took around 17 seconds. 
> > 
> > So to me above test results suggest that this patch does not worsen
> > the performance. In fact it helps. (at least on ext3 file system.)
> > 
> > Not sure why are you seeing different results with XFS.
> 
> So why didn't you test it with XFS to verify his results?

Just got little lazy. Find the testing results with ext3, ext4 and
xfs below.

>  We all know
> that different filesystems have different I/O patters, and we have
> a history of really nasty regressions in one filesystem by good meaning
> changes to the I/O scheduler.
> 
> ext3 in fact is a particularly bad test case as it not only doesn't have
> I/O barriers enabled, but also has particularly bad I/O patterns
> compared to modern filesystems.

Ext3 results
============
ext3 (2.6.35-rc6)	ext3 (35-rc6-fsync)
-----------------	-------------------
fsync time: 3.4173	fsync time: 0.0171
fsync time: 0.8831	fsync time: 0.0951
fsync time: 0.6985	fsync time: 0.0848
fsync time: 8.9449	fsync time: 0.1206
fsync time: 4.3075	fsync time: 0.4150
fsync time: 6.0146	fsync time: 0.0856
fsync time: 9.7134	fsync time: 0.1151
fsync time: 9.2247	fsync time: 0.1083
fsync time: 6.5061	fsync time: 0.1218
fsync time: 6.1862	fsync time: 4.1666
fsync time: 6.1136	fsync time: 0.1075
fsync time: 3.3593	fsync time: 0.3442
fsync time: 4.3309	fsync time: 0.1062
fsync time: 2.3596	fsync time: 2.8502
fsync time: 0.0151	fsync time: 0.0433
fsync time: 0.0180	fsync time: 4.0526
fsync time: 0.3685	fsync time: 0.1819
fsync time: 2.7396	fsync time: 0.1479
fsync time: 3.1537	fsync time: 0.1480
fsync time: 2.4474	fsync time: 0.1715
fsync time: 2.7085	fsync time: 0.0079
fsync time: 3.1629	fsync time: 0.0181
fsync time: 2.9186	fsync time: 0.0134

XFS results
==========
XFS (2.6.35-rc6)	XFS (with fsync patch)
fsync time: 5.0746	fsync time: 1.8025
fsync time: 3.0057	fsync time: 2.3392
fsync time: 3.0960	fsync time: 2.2810
fsync time: 2.8392	fsync time: 2.2894
fsync time: 2.4901	fsync time: 2.3059
fsync time: 2.3151	fsync time: 2.3061
fsync time: 2.3066	fsync time: 2.9825
fsync time: 0.6608	fsync time: 2.3144
fsync time: 0.0595	fsync time: 2.2894
fsync time: 2.0977	fsync time: 0.0508
fsync time: 2.3236	fsync time: 2.3396
fsync time: 2.3229	fsync time: 2.3310
fsync time: 2.3065	fsync time: 2.3061
fsync time: 2.3234	fsync time: 2.3060
fsync time: 2.3150	fsync time: 2.3561
fsync time: 2.3149	fsync time: 2.3313
fsync time: 2.3234	fsync time: 2.0221
fsync time: 2.3066	fsync time: 2.2891
fsync time: 2.3232	fsync time: 2.3144
fsync time: 2.3317	fsync time: 2.3144
fsync time: 2.3321	fsync time: 2.2894
fsync time: 2.3232	fsync time: 2.3228
fsync time: 0.0514	fsync time: 2.3144
fsync time: 2.2480	fsync time: 0.0506

Ext4
====
ext4 (vanilla)		ext4 (patched)
fsync time: 3.4080	fsync time: 2.9109
fsync time: 17.8330	fsync time: 25.0503
fsync time: 0.0922	fsync time: 2.5495
fsync time: 0.0710	fsync time: 0.0943
fsync time: 19.7977	fsync time: 0.0770
fsync time: 20.6592	fsync time: 16.3287
fsync time: 0.1020	fsync time: 24.4983
fsync time: 0.0689	fsync time: 0.1006
fsync time: 19.9981	fsync time: 0.0783
fsync time: 20.6605	fsync time: 19.1181
fsync time: 0.0930	fsync time: 22.0860
fsync time: 0.0776	fsync time: 0.0909


Notes:
======
- Above results are with and without corrado's fsync issue patch. We
  happen to be discussing it in a different thread though, hence
  specifying it specifically.

- I am running linus torture test and also running ted so's fsync-tester
  to monitor fsync latencies.

- Looks like ext3 fsync times have improved.
- XFS fsync times have remained unchanged.
- ext4 fsync times seems to have gone up a bit.

I used default mount options. So I am assuming high fsync times of ext4
comes from the fact that barriers much be enabled by default. Will do
some blktracing on ext4 case tomorrow, otherwise I think this patch
looks good.

Thanks
Vivek