Re: Abysmal Performance

[Josef Bacik <josef@redhat.com>]

On 06/22/2011 11:57 AM, Calvin Walton wrote:
> On Wed, 2011-06-22 at 11:39 -0400, Josef Bacik wrote:
>> On 06/22/2011 10:15 AM, Henning Rohlfs wrote:
>>> On Tue, 21 Jun 2011 11:24:11 -0400, Calvin Walton wrote:
>>>> On Mon, 2011-06-20 at 23:51 +0200, Henning Rohlfs wrote:
>>>>> Hello,
>>>>>
>>>>>  I've migrated my system to btrfs (raid1) a few months ago. Since=
 then
>>>>>  the performance has been pretty bad, but recently it's gotten
>>>>>  unbearable: a simple sync called while the system is idle can ta=
ke
>>>>> 20 up
>>>>>  to 60 seconds. Creating or deleting files often has several seco=
nds
>>>>>  latency, too.
>>>>
>>>> I think I=E2=80=99ve been seeing a fairly similar, or possibly the=
 same? issue
>>>> as well. It looks like it=E2=80=99s actually a regression introduc=
ed in 2.6.39 -
>>>> if I switch back to a 2.6.38 kernel, my latency issues magically g=
o
>>>> away! (I'm curious: does using the older 2.6.38.x kernel help with
>>>> anyone else that's seeing the issue?)
>=20
>>>> I think I can reproduce the issue well enough to bisect it, so I m=
ight
>>>> give that a try. It'll be slow going, though.
>>>
>>> You are right. This seems to be a regression in the .39 kernel. I t=
ested
>>> with 2.6.38.2 just now and the performance is back to normal.
>>
>> Would you mind bisecting?
>=20
> Just before I was going to try bisecting, I tried the 3.0-rc4 kernel =
out
> of curiosity. And it seems to be quite a bit better; at the very leas=
t,
> I=E2=80=99m not seeing gui applications stalling for ~10 seconds when=
 doing
> things like opening or writing files. Latencytop is reporting fsync()
> latencies staying pretty steady in the range of under 300ms, with
> occasional outliers at up to 2s, and it's not getting worse with time=
=2E
>=20
> I'll still look into doing a bisect between 2.6.38 and 2.6.39, I'm
> curious what went wrong.
>=20

Yeah that makes two of us :).  There were some other plugging changes
that went into to 38, so maybe bisect all of the kernel, not just fs/
just in case it was those and not us.  Thanks,

Josef
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