linux-kernel - Re: Poor PostgreSQL scaling on Linux 2.6.25-rc5 (vs 2.6.22)

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Date:	Tue, 11 Mar 2008 22:34:08 +0100
From:	Cyrus Massoumi <cyrusm@....net>
To:	Nicholas Miell <nmiell@...cast.net>
CC:	Nick Piggin <nickpiggin@...oo.com.au>,
	"Molnar, Ingo" <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Poor PostgreSQL scaling on Linux 2.6.25-rc5 (vs 2.6.22)

Nicholas Miell wrote:
> On Tue, 2008-03-11 at 17:49 +1100, Nick Piggin wrote:
> 
>> So PostgreSQL performance profile is actually much more interesting.
>> To my dismay, I found that Linux 2.6.25-rc5 performs really badly
>> after saturating the runqueues and subsequently increasing threads.
>> 2.6.22 drops a little bit, but basically settles near the peak
>> performance. With 2.6.25-rc5, throughput seems to be falling off
>> linearly with the number of threads.
>>
> 
> The FreeBSD folks have a whole host of benchmark results (MySQL,
> PostgreSQL, BIND, NSD, ebizzy, SPECjbb, etc.) located at
> http://people.freebsd.org/~kris/scaling/ that demonstrate that the
> 2.6.23+ scheduler is worse than the 2.6.22 scheduler and both are worse
> than FreeBSD 7.
> 
> The interesting thing is that they've been running these tests
> constantly for years now to demonstrate that their new scheduler hasn't
> regressed compared to their old scheduler and as a benchmark against the
> competition (i.e. Linux).
> 
> Does anybody even do this at all for Linux?
> 
> (Also, ignoring MySQL because it's a terrible piece of software at least
> when regarding it's scalability is a bad idea. It's the M in LAMP, it
> has a huge user base, and FreeBSD manages to outperform Linux with the
> same unscalable piece of software.)

Did you actually see this? 
http://www.kernel.org/pub/linux/kernel/people/npiggin/sysbench/

FreeBSD does not outperform Linux, it's actually a bit faster according 
to Nick's tests.

I cannot comment on BIND and NSD, but SPECjbb looks pretty close and the 
bad ebizzy performance seems to be an issue with glibc's memory allocator.


greetings
Cyrus

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