linux-kernel - Re: SMP performance degradation with sysbench

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Date:	Tue, 13 Mar 2007 16:11:02 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Anton Blanchard <anton@...ba.org>
CC:	Rik van Riel <riel@...hat.com>,
	Lorenzo Allegrucci <l_allegrucci@...oo.it>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: SMP performance degradation with sysbench

Anton Blanchard wrote:
>  
> Hi Nick,
> 
> 
>>Anyway, I'll keep experimenting. If anyone from MySQL wants to help look
>>at this, send me a mail (eg. especially with the sched_setscheduler issue,
>>you might be able to do something better).
> 
> 
> I took a look at this today and figured Id document it:
> 
> http://ozlabs.org/~anton/linux/sysbench/
> 
> Bottom line: it looks like issues in the glibc malloc library, replacing
> it with the google malloc library fixes the negative scaling:
> 
> # apt-get install libgoogle-perftools0
> # LD_PRELOAD=/usr/lib/libtcmalloc.so /usr/sbin/mysqld

Hi Anton,

Very cool. Yeah I had come to the conclusion that it wasn't a kernel
issue, and basically was afraid to look into userspace ;)

That bogus setscheduler thing must surely have never worked, though.
I wonder if FreeBSD avoids the scalability issue because it is using
SCHED_RR there, or because it has a decent threaded malloc implementation.

-- 
SUSE Labs, Novell Inc.
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