linux-kernel - Re: SMP performance degradation with sysbench

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Message-ID: <45E439E4.5030703@redhat.com>
Date:	Tue, 27 Feb 2007 09:02:12 -0500
From:	Rik van Riel <riel@...hat.com>
To:	"J.A. Magallón" <jamagallon@....com>
CC:	Hiro Yoshioka <hyoshiok@...aclelinux.com>, davej@...hat.com,
	harlan@...select.com, nickpiggin@...oo.com.au,
	l_allegrucci@...oo.it, linux-kernel@...r.kernel.org, mingo@...e.hu,
	suparna@...ibm.com, jens.axboe@...cle.com
Subject: Re: SMP performance degradation with sysbench

J.A. Magallón wrote:
> On Mon, 26 Feb 2007 23:31:29 -0500, Rik van Riel <riel@...hat.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.

-- 
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.
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