Re: SMP performance degradation with sysbench

From: Robert Hancock <hancockr@shaw.ca>
To: hyoshiok@miraclelinux.com
Cc: Dave Jones <davej@redhat.com>, Pete Harlan <harlan@artselect.com>,
	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
Date: Tue, 27 Feb 2007 18:20:25 -0600	[thread overview]
Message-ID: <45E4CAC9.4070504@shaw.ca> (raw)
In-Reply-To: <fa.XocsudxlGplKh0kloTtA0juPwtA@ifi.uio.no>

Hiro Yoshioka wrote:
> Howdy,
> 
> MySQL 5.0.26 had some scalability issues and it solved since 5.0.32
> http://ossipedia.ipa.go.jp/capacity/EV0612260303/
> (written in Japanese but you may read the graph. We compared
> 5.0.24 vs 5.0.32)
> 
> The following is oprofile data
> ==> 
> cpu=8-mysql=5.0.32-gcc=3.4/oprofile-eu=2200-op=default-none/opreport-l.txt
> <==
> CPU: Core Solo / Duo, speed 2666.76 MHz (estimated)
> Counted CPU_CLK_UNHALTED events (Unhalted clock cycles) with a unit
> mask of 0x00 (Unhalted core cycles) count 100000
> samples  %        app name                 symbol name
> 47097502 16.8391  libpthread-2.3.4.so      pthread_mutex_trylock
> 19636300  7.0207  libpthread-2.3.4.so      pthread_mutex_unlock
> 18600010  6.6502  mysqld                   rec_get_offsets_func
> 18121328  6.4790  mysqld                   btr_search_guess_on_hash
> 11453095  4.0949  mysqld                   row_search_for_mysql
> 
> MySQL tries to get a mutex but it spends about 16.8% of CPU on 8 core
> machine.

Curious that it calls pthread_mutex_trylock (as opposed to 
pthread_mutex_lock) so often. Maybe they're doing some kind of mutex 
lock busy-looping?

-- 
Robert Hancock      Saskatoon, SK, Canada
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