Re: xfs, 2.6.27=>.32 sync write 10 times slowdown [was: xfs, aacraid2.6.27 => 2.6.32 results in 6 times slowdown]

From: Michael Tokarev
Date: Wed Jun 09 2010 - 15:12:03 EST

09.06.2010 11:47, Dave Chinner wrote:
On Wed, Jun 09, 2010 at 10:43:37AM +0400, Michael Tokarev wrote:
09.06.2010 03:18, Dave Chinner wrote:
On Wed, Jun 09, 2010 at 12:34:00AM +0400, Michael Tokarev wrote:
Simple test doing random reads or writes of 4k blocks in a 1Gb
file located on an xfs filesystem, Mb/sec:

sync direct
read write write
2.6.27 xfs 1.17 3.69 3.80
2.6.32 xfs 1.26 0.52 5.10
2.6.32 ext3 1.19 4.91 5.02

Out of curiousity, what does 2.6.34 get on this workload?

2.6.34 works quite well:
2.6.34 xfs 1.14 4.75 5.00

The same is with -o osyncisosync (in .34). Actually,
osyncis[od]sync mount options does not change anything, not
in .32 nor in .34.

Also, what happens if you test with noop or deadline scheduler,
rather than cfq (or whichever one you are using)? i.e. is this a
scheduler regression rather than a filesystem issue?

Using deadline. Switching to noop makes no difference whatsoever.

Also, a block trace of the sync write workload on both .27 and .32
would be interesting to see what the difference in IO patterns is...

I see. Will try to collect them. With the limited timeframe I have
to do any testing.

Well, I normally just create a raid0 lun per disk in those cases,
hence the luns present the storage to linux as a JBOD....

That's, um, somewhat ugly :)

I also experimented with both O_SYNC|O_DIRECT: it is as slow as
without O_DIRECT, i.e. O_SYNC makes whole thing slow regardless
of other options.

So it's the inode writeback that is causing the slowdown. We've
recently changed O_SYNC semantics to be real O_SYNC, not O_DSYNC
as .27 is. I can't remember if that was in 2.6.32 or not, but
there's definitely a recent change to O_SYNC behaviouri that would
cause this...

But there are two mount options that seems to control this behavour:
osyncisosync and osyncisdsync. Neither of which - seemingly - makes
no difference.

related to block devices or usage of barriers. For XFS it always
mounts like this:

SGI XFS with ACLs, security attributes, large block/inode numbers, no debug enabled
SGI XFS Quota Management subsystem
XFS mounting filesystem sda6

So barriers are being issued.

They _are_ being issued, I knew it from the start. What I asked
several times is if there's a way to know if they're _hitting_ the
actual low-level device (disk or raid controller). This is entirely
different story... ;)

and for the device in question, it is always like

Adaptec aacraid driver 1.1-5[2456]-ms
aacraid 0000:03:01.0: PCI INT A -> GSI 24 (level, low) -> IRQ 24
AAC0: kernel 5.1-0[8832] Feb 1 2006

Old firmware. An update might help.

Well, it worked just fine in .27. So far I see some problem in kernel,
not in controller [firmware]... ;)

Thank you !

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