linux-kernel - Re: SMP performance degradation with sysbench

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Date:	Tue, 13 Mar 2007 07:00:27 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Anton Blanchard <anton@...ba.org>
CC:	Nick Piggin <nickpiggin@...oo.com.au>,
	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 a écrit :
>  
> 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, thanks for the report.
glibc has certainly many scalability problems.

One of the known problem is its (ab)use of mmap() to allocate one (yes : one 
!) page every time you fopen() a file. And then a munmap() at fclose() time.

mmap()/munmap() should be avoided as hell in multithreaded programs.
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