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Subject: Re: SMP performance degradation with sysbench
From: Lorenzo Allegrucci <l_allegrucci@yahoo.it>
To: Rik van Riel <riel@redhat.com>
Cc: "\"J.A." =?ISO-8859-1?Q?Magall=F3n=22?= <jamagallon@ono.com>,
       Hiro Yoshioka <hyoshiok@miraclelinux.com>, davej@redhat.com,
       harlan@artselect.com, nickpiggin@yahoo.com.au,
       linux-kernel@vger.kernel.org, mingo@elte.hu, suparna@in.ibm.com,
       jens.axboe@oracle.com
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Date: Tue, 27 Feb 2007 20:05:27 +0100
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On Tue, 2007-02-27 at 09:02 -0500, Rik van Riel wrote:
> J.A. Magallón wrote:
> > On Mon, 26 Feb 2007 23:31:29 -0500, Rik van Riel <riel@redhat.com> wrote:
> > 
> >> Hiro Yoshioka wrote:
> 
> >>> Another question. When the number of threads exceeds the number of
> >>> CPU cores, we may get a lot of idle time. Then a workaround of
> >>> MySQL is that do not creat threads which exceeds the number
> >>> of CPU cores. Is it right?
> >> Not really, that would make it impossible for MySQL to
> >> handle more simultaneous database queries than the system
> >> has CPUs.
> >>
> > 
> > I don't know myqsl internals, but you assume one thread per query.
> > If its more like Apache, one long living thread for several connections ?
> 
> Yes, they are longer lived client connections.  One thread
> per connection, just like Apache.
> 
> > Its the same to answer 4+4 queries than 8 at half the speed, isn't it ?
> 
> That still doesn't fix the potential Linux problem that this
> benchmark identified.
> 
> To clarify: I don't care as much about MySQL performance as
> I care about identifying and fixing this potential bug in
> Linux.

Here http://people.freebsd.org/~kris/scaling/mysql.html Kris Kennaway
talks about a patch for FreeBSD 7 which addresses poor scalability
of file descriptor locking and that it's responsible for almost all
of the performance and scaling improvements.


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