Re: Ext4 performance regression: Post 2.6.30

[Eric Sandeen <sandeen@redhat.com>]

Keith Mannthey wrote:
> On Mon, 2010-03-29 at 11:10 -0400, Greg Freemyer wrote:
>> On Mon, Mar 29, 2010 at 2:25 AM, Keith Mannthey <kmannth@us.ibm.com> wrote:
>>>
>>> After 2.6.30 I am seeing large performance regressions on a raid setup.
>>> I am working to publish a larger amount of data but I wanted to get some
>>> quick data out about what I am seeing.
>>>
>> Is mdraid involved?
>>
>> They added barrier support for some configs after 2.6.30 I believe.
>> It can cause a drastic perf change, but it increases reliability and
>> is "correct".
> 
> lvm and device mapper are is involved.  The git bisect just took me to:
> 
> 374bf7e7f6cc38b0483351a2029a97910eadde1b is first bad commit
> commit 374bf7e7f6cc38b0483351a2029a97910eadde1b
> Author: Mikulas Patocka <mpatocka@redhat.com>
> Date:   Mon Jun 22 10:12:22 2009 +0100
> 
>     dm: stripe support flush
>     
>     Flush support for the stripe target.
>     
>     This sets ti->num_flush_requests to the number of stripes and
>     remaps individual flush requests to the appropriate stripe devices.
>     
>     Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
>     Signed-off-by: Alasdair G Kergon <agk@redhat.com>
> 
> :040000 040000 542f4b9b442d1371c6534f333b7e00714ef98609 d490479b660139fc1b6b0ecd17bb58c9e00e597e M	drivers
> 
> 
> This may be correct behavior but the performance penalty in this test
> case is pretty high. 
> 
> I am going to move back to current kernels and starting looking into
> ext4/dm flushing. 

It would probably be interesting to do a mount -o nobarrier to see if
that makes the regression go away.

-Eric

> Thanks,
>   Keith Mannthey