Re: Ext4 performance regression: Post 2.6.30

[Keith Mannthey <kmannth@us.ibm.com>]

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. 

Thanks,
  Keith Mannthey