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qmail preprocessing slower with current Linux kernels ?

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brunni at netestate

Apr 10, 2012, 5:58 AM

Post #1 of 3 (671 views)
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qmail preprocessing slower with current Linux kernels ?

hi all

I have a Linux system I can boot with kernel 2.6.36.3 or 3.2.5 (the same
filesystem is mounted). The .config file from 2.6.36.3 was used for compiling
3.2.5.

The filesystem is a md raid1 with reiserfs. I can write sequentially with
32-33MB/s from both kernels to it.

The system runs netqmail-1.05 and just had ca. 8000 mails in the queue that
were "not yet preprocessed". I tried both kernels several times on this queue
for some time and found out that preprocessing is more than 3 times faster
on 2.6.36.3 (>30 mails/s) as with the default 3.2.5 kernel (ca. 10 mails/s).
Resource utilization as seen with top was not critical with both kernels but
the Blk_wrtn/s value from iostat was ca. 3 time higher with 2.6.36.3.

I run the same 3.2.5 kernel on 17 other systems and did not notice a
performance slowdown with other applications.

Is there a possibility that this slowdown is qmail related ? Does anyone have
a clue ?

Regards,

Michael Brunnbauer

--
++ Michael Brunnbauer
++ netEstate GmbH
++ Geisenhausener Straße 11a
++ 81379 München
++ Tel +49 89 32 19 77 80
++ Fax +49 89 32 19 77 89
++ E-Mail brunni [at] netestate
++ http://www.netestate.de/
++
++ Sitz: München, HRB Nr.142452 (Handelsregister B München)
++ USt-IdNr. DE221033342
++ Geschäftsführer: Michael Brunnbauer, Franz Brunnbauer
++ Prokurist: Dipl. Kfm. (Univ.) Markus Hendel

ma1l1ists at yahoo

Apr 10, 2012, 1:26 PM

Post #2 of 3 (620 views)
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Re: qmail preprocessing slower with current Linux kernels ? [In reply to]

On Tue, 10 Apr 2012 14:58:10 +0200
Michael Brunnbauer wrote:

> Is there a possibility that this slowdown is qmail related ? Does anyone have
> a clue ?

There was a kernel bug causing a filesystem caching slow down. I don't
remember which 3.x it applied to.

I'd try building the 3.2.14 and see if that fixes it.

brunni at netestate

Apr 11, 2012, 2:02 AM

Post #3 of 3 (625 views)
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Re: qmail preprocessing slower with current Linux kernels ? [In reply to]

Hello Kevin,

On Tue, Apr 10, 2012 at 09:26:09PM +0100, Kevin Chadwick wrote:
> There was a kernel bug causing a filesystem caching slow down. I don't
> remember which 3.x it applied to.
>
> I'd try building the 3.2.14 and see if that fixes it.

Thanks for the tip. I tried but 3.2.14 does not make things faster.

Regards,

Michael Brunnbauer

--
++ Michael Brunnbauer
++ netEstate GmbH
++ Geisenhausener Straße 11a
++ 81379 München
++ Tel +49 89 32 19 77 80
++ Fax +49 89 32 19 77 89
++ E-Mail brunni [at] netestate
++ http://www.netestate.de/
++
++ Sitz: München, HRB Nr.142452 (Handelsregister B München)
++ USt-IdNr. DE221033342
++ Geschäftsführer: Michael Brunnbauer, Franz Brunnbauer
++ Prokurist: Dipl. Kfm. (Univ.) Markus Hendel

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