Btrfs devel - Nov 2012 - problem with ceph and btrfs patch: set journal_info in async trans commit worker

Hello list,

i wanted to try out ceph with latest vanilla kernel 3.7-rc5. I was 
seeing a massive performance degration. I see around 22x 
btrfs-endio-write processes every 10-20 seconds and they run a long time 
while consuming a massive amount of CPU.

So my performance of 23.000 iops drops to an up and down of 23.000 iops 
to 0 - avg is now 2500 iops instead of 23.000.

Git bisect shows me commit: e209db7ace281ca347b1ac699bf1fb222eac03fe 
"Btrfs: set journal_info in async trans commit worker" as the 
problematic patch.

When i revert this one everything is fine again.

Is this known?

Greets,
Stefan
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Hi, Stefan

On wed, 14 Nov 2012 14:42:07 +0100, Stefan Priebe - Profihost AG
wrote:
> Hello list,
> 
> i wanted to try out ceph with latest vanilla kernel 3.7-rc5. I was seeing a
massive performance degration. I see around 22x btrfs-endio-write processes
every 10-20 seconds and they run a long time while consuming a massive amount of
CPU.
> 
> So my performance of 23.000 iops drops to an up and down of 23.000 iops to
0 - avg is now 2500 iops instead of 23.000.
> 
> Git bisect shows me commit: e209db7ace281ca347b1ac699bf1fb222eac03fe
"Btrfs: set journal_info in async trans commit worker" as the
problematic patch.
> 
> When i revert this one everything is fine again.
> 
> Is this known?
Could you try the following patch?

http://marc.info/?l=linux-btrfs&m=135175512030453&w=2

I think the patch

  Btrfs: set journal_info in async trans commit worker

is not the real reason that caused the regression.

I guess it is caused by the bug of the reservation. When we join the
same transaction handle more than 2 times, the pointer of the reservation
in the transaction handle would be lost, and the statistical data in the
reservation would be corrupted. And then we would trigger the space flush,
which may block your tasks.

Thanks
Miao
> 
> Greets,
> Stefan
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Hi Miao,

Am 15.11.2012 06:18, schrieb Miao Xie:
> Hi, Stefan
>
> On wed, 14 Nov 2012 14:42:07 +0100, Stefan Priebe - Profihost AG wrote:
>> Hello list,
>>
>> i wanted to try out ceph with latest vanilla kernel 3.7-rc5. I was
seeing a massive performance degration. I see around 22x btrfs-endio-write
processes every 10-20 seconds and they run a long time while consuming a massive
amount of CPU.
>>
>> So my performance of 23.000 iops drops to an up and down of 23.000 iops
to 0 - avg is now 2500 iops instead of 23.000.
>>
>> Git bisect shows me commit: e209db7ace281ca347b1ac699bf1fb222eac03fe
"Btrfs: set journal_info in async trans commit worker" as the
problematic patch.
>>
>> When i revert this one everything is fine again.
>>
>> Is this known?
>
> Could you try the following patch?
>
> http://marc.info/?l=linux-btrfs&m=135175512030453&w=2
>
> I think the patch
>
>    Btrfs: set journal_info in async trans commit worker
>
> is not the real reason that caused the regression.
>
> I guess it is caused by the bug of the reservation. When we join the
> same transaction handle more than 2 times, the pointer of the reservation
> in the transaction handle would be lost, and the statistical data in the
> reservation would be corrupted. And then we would trigger the space flush,
> which may block your tasks.
i applied your whole patchset. It looks a lot better now but avg iops is 
now 5000 iops and not 23.000 like when removing the mentioned commit 
(e209db7ace281ca347b1ac699bf1fb222eac03fe).

Stefan
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