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Date: Tue, 13 Mar 2007 07:00:27 +0100
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Anton Blanchard <anton@samba.org>
CC: Nick Piggin <nickpiggin@yahoo.com.au>, Rik van Riel <riel@redhat.com>,
       Lorenzo Allegrucci <l_allegrucci@yahoo.it>,
       linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
       Suparna Bhattacharya <suparna@in.ibm.com>,
       Jens Axboe <jens.axboe@oracle.com>
Subject: Re: SMP performance degradation with sysbench
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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.