Ext4 performance regression: Post 2.6.30

Ext4 performance regression: Post 2.6.30

[Keith Mannthey]

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. 

The test (FFSB test suite) I am running is basically random direct io
writes.  The below data is from 128 threads all doing these random
writes. 1 and 32 thread results are not as drastically bad but 2.6.30
has the strongest results.  

  Under a mailserver workload I see similar performance impacts at this
same kernel change point.  I hope to publish better data soon.  Several
other workload types do not show this performance regression. 
 

2.6.30:

Total Results
===============
             Op Name   Transactions	 Trans/sec	% Trans	    % Op Weight
Throughput
             =======   ============	 =========	=======	    ===========
==========
               write :      9015040	  29561.46	100.000%		100.000%
115MB/sec
-
29561.46 Transactions per Second


Any kernel past 2.6.30.  This is from 2.6.31-rc1:

Total Results
===============
             Op Name   Transactions	 Trans/sec	% Trans	    % Op Weight
Throughput
             =======   ============	 =========	=======	    ===========
==========
               write :      3185920	  10120.50	100.000%		100.000%
39.5MB/sec

Re: Ext4 performance regression: Post 2.6.30

[Greg Freemyer]

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".

Greg

Re: Ext4 performance regression: Post 2.6.30

[Keith Mannthey]

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
 

Re: Ext4 performance regression: Post 2.6.30

[Eric Sandeen]

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

Re: Ext4 performance regression: Post 2.6.30

[Keith Mannthey]

On Tue, 2010-03-30 at 23:06 -0500, Eric Sandeen wrote:
> 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.

-o nobarrier takes the regression away with 2.6.34-rc3:

Default mount: ~27500

-o nobarrier: ~12500 

Barriers on this setup cost ALOT during writes.  

Interestingly as well the "mailserver" workload regression is also
removed by mounting with "-o nobarrier". 

I am going to see what impact is seen on a single disk setup. 

Thanks,
  Keith Mannthey
  LTC FS-Dev 

Re: Ext4 performance regression: Post 2.6.30

[Greg Freemyer]

On Wed, Mar 31, 2010 at 6:02 PM, Keith Mannthey <kmannth@us.ibm.com> wrote:
> On Tue, 2010-03-30 at 23:06 -0500, Eric Sandeen wrote:
>> 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.
>
> -o nobarrier takes the regression away with 2.6.34-rc3:
>
> Default mount: ~27500
>
> -o nobarrier: ~12500
>
> Barriers on this setup cost ALOT during writes.
>
> Interestingly as well the "mailserver" workload regression is also
> removed by mounting with "-o nobarrier".
>
> I am going to see what impact is seen on a single disk setup.
>
> Thanks,
>  Keith Mannthey
>  LTC FS-Dev

I'm curious if your using an internal or external journal?

I'd guess the cost of barriers is much greater with an internal
journal, but I don't recall seeing any benchmarks one way or the
other.

Greg
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Re: Ext4 performance regression: Post 2.6.30

[Keith Mannthey]

On Wed, 2010-03-31 at 18:06 -0400, Greg Freemyer wrote:
> On Wed, Mar 31, 2010 at 6:02 PM, Keith Mannthey <kmannth@us.ibm.com> wrote:
> > On Tue, 2010-03-30 at 23:06 -0500, Eric Sandeen wrote:
> >> 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.
> >
> > -o nobarrier takes the regression away with 2.6.34-rc3:
> >
> > Default mount: ~27500
> >
> > -o nobarrier: ~12500
> >
> > Barriers on this setup cost ALOT during writes.
> >
> > Interestingly as well the "mailserver" workload regression is also
> > removed by mounting with "-o nobarrier".
> >
> > I am going to see what impact is seen on a single disk setup.
> >
> > Thanks,
> >  Keith Mannthey
> >  LTC FS-Dev
> 
> I'm curious if your using an internal or external journal?

I am unsure.  How do I tell?  I am using defaults except with the -o
nobarrier.   I know jdb2 is being used. 

Thanks,
  Keith 

> I'd guess the cost of barriers is much greater with an internal
> journal, but I don't recall seeing any benchmarks one way or the
> other.
> 
> Greg

Re: Ext4 performance regression: Post 2.6.30

[Greg Freemyer]

On Wed, Mar 31, 2010 at 6:14 PM, Keith Mannthey <kmannth@us.ibm.com> wrote:
> On Wed, 2010-03-31 at 18:06 -0400, Greg Freemyer wrote:
>> On Wed, Mar 31, 2010 at 6:02 PM, Keith Mannthey <kmannth@us.ibm.com> wrote:
>> > On Tue, 2010-03-30 at 23:06 -0500, Eric Sandeen wrote:
>> >> 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.
>> >
>> > -o nobarrier takes the regression away with 2.6.34-rc3:
>> >
>> > Default mount: ~27500
>> >
>> > -o nobarrier: ~12500
>> >
>> > Barriers on this setup cost ALOT during writes.
>> >
>> > Interestingly as well the "mailserver" workload regression is also
>> > removed by mounting with "-o nobarrier".
>> >
>> > I am going to see what impact is seen on a single disk setup.
>> >
>> > Thanks,
>> >  Keith Mannthey
>> >  LTC FS-Dev
>>
>> I'm curious if your using an internal or external journal?
>
> I am unsure.  How do I tell?  I am using defaults except with the -o
> nobarrier.   I know jdb2 is being used.
>
> Thanks,
>  Keith

The default is internal.  External requires a separate partition be
provided to hold the journal.

Since journals are typically very small relative to the overall
filesystem, a small raid 1 partition would be my production
recommendation to hold an external journal.

But for performance testing purposes, if you have a drive that is not
participating in your current raid setup, you can simply create a
small partition on it and use it to hold the external journal.  I
believe you can convert your existing file system to an external
journal easily and without having to recreate your file system.

Greg
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