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From: "J.A. Magallón" <jamagallon@ono.com>
To: Rik van Riel <riel@redhat.com>
Cc: Hiro Yoshioka <hyoshiok@miraclelinux.com>,
	davej@redhat.com, harlan@artselect.com, nickpiggin@yahoo.com.au,
	l_allegrucci@yahoo.it, linux-kernel@vger.kernel.org,
	mingo@elte.hu, suparna@in.ibm.com, jens.axboe@oracle.com
Subject: Re: SMP performance degradation with sysbench
Date: Tue, 27 Feb 2007 09:14:09 +0100	[thread overview]
Message-ID: <20070227091409.6f3d12f9@werewolf-wl> (raw)
In-Reply-To: <45E3B421.603@redhat.com>

On Mon, 26 Feb 2007 23:31:29 -0500, Rik van Riel <riel@redhat.com> wrote:

> Hiro Yoshioka wrote:
> > Hi,
> > 
> > From: Rik van Riel <riel@redhat.com>
> >> 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)
> > snip
> >>> MySQL tries to get a mutex but it spends about 16.8% of CPU on 8 core
> >>> machine.
> >>>
> >>> I think there are a lot of room to be inproved in MySQL implementation.
> >> That's one aspect.
> >>
> >> The other aspect of the problem is that when the number of
> >> threads exceeds the number of CPU cores, Linux no longer
> >> manages to keep the CPUs busy and we get a lot of idle time.
> >>
> >> On the other hand, with the number of threads being equal to
> >> the number of CPU cores, we are 100% CPU bound...
> > 
> > I have a question. If so, what is the difference of kernel's
> > view between SMP and CPU cores?
> 
> None.  Each schedulable entity (whether a fully fledged
> CPU core or an SMT/HT thread) is treated the same.
> 

And what do the SMT and Multi-Core scheduling options in the kernel
config are for ?  Because of this thread I re-read the help text, and
it looks like on could de-select the SMT scheduler option, get a
working SMP system, and see what difference ? I suppose its related
to migration and cache flushing and so on, but where could I get
more details ?
And more strange, what is the difference between multi-core and
normal SMP configs ?

> > 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 ?
Its the same to answer 4+4 queries than 8 at half the speed, isn't it ?

> Besides, it looks like this is not a problem in MySQL
> per se (it works on FreeBSD) but some bug in Linux.
> 


--
J.A. Magallon <jamagallon()ono!com>     \               Software is like sex:
                                         \         It's better when it's free
Mandriva Linux release 2007.1 (Cooker) for i586
Linux 2.6.19-jam07 (gcc 4.1.2 20070115 (prerelease) (4.1.2-0.20070115.1mdv2007.1)) #2 SMP PREEMPT

  reply	other threads:[~2007-02-27  8:14 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-25 17:44 Lorenzo Allegrucci
2007-02-25 23:46 ` Rik van Riel
2007-02-26 13:36   ` Nick Piggin
2007-02-26 13:41     ` Nick Piggin
2007-02-26 22:04     ` Pete Harlan
2007-02-26 22:36       ` Dave Jones
2007-02-27  0:32         ` Hiro Yoshioka
2007-02-27  0:43           ` Rik van Riel
2007-02-27  4:03             ` Hiro Yoshioka
2007-02-27  4:31               ` Rik van Riel
2007-02-27  8:14                 ` J.A. Magallón [this message]
2007-02-27 14:02                   ` Rik van Riel
2007-02-27 14:56                     ` Paulo Marques
2007-02-27 20:40                       ` Nish Aravamudan
2007-02-28  2:21                       ` Bill Davidsen
2007-02-28  2:52                         ` Nish Aravamudan
2007-03-01  0:20                           ` Nish Aravamudan
2007-02-27 19:05                     ` Lorenzo Allegrucci
2007-03-01 16:57                       ` Lorenzo Allegrucci
2007-02-28  1:27     ` Nish Aravamudan
2007-02-28  2:22       ` Nick Piggin
2007-02-28  2:51         ` Nish Aravamudan
2007-03-12 22:00     ` Anton Blanchard
2007-03-13  5:11       ` Nick Piggin
2007-03-13  9:45         ` Andrea Arcangeli
2007-03-13 10:06           ` Nick Piggin
2007-03-13 10:31             ` Andrea Arcangeli
2007-03-13 10:37               ` Nick Piggin
2007-03-13 10:57                 ` Andrea Arcangeli
2007-03-13 11:12                   ` Nick Piggin
2007-03-13 11:40                     ` Eric Dumazet
2007-03-13 11:56                       ` Nick Piggin
2007-03-13 11:42                     ` Andrea Arcangeli
2007-03-13 12:02                       ` Eric Dumazet
2007-03-13 12:27                         ` Jakub Jelinek
2007-03-13 12:08                       ` Nick Piggin
2007-03-14 23:33                         ` Siddha, Suresh B
2007-03-20  2:29                           ` Zhang, Yanmin
2007-04-02  2:59                             ` Zhang, Yanmin
2007-03-13  6:00       ` Eric Dumazet
2007-03-14  0:36       ` Nish Aravamudan
2007-03-14  1:00         ` Eric Dumazet
2007-03-14  1:09           ` Nish Aravamudan
     [not found] <fa.V3M3ZgXL+lFlIyhx43YxCU/JFUk@ifi.uio.no>
     [not found] ` <fa.ciL5lzdfskdJHJPgn+UVCHt/9EM@ifi.uio.no>
     [not found]   ` <fa.2ABbHhyCbp3Fx7hSE/Gr0SuzFvw@ifi.uio.no>
     [not found]     ` <fa.oaZk6Aiqd8gyZNsj7+m+w9MibhU@ifi.uio.no>
     [not found]       ` <fa.RjX9Y4ckjRCle5L+uWNdd0snOio@ifi.uio.no>
     [not found]         ` <fa.XocsudxlGplKh0kloTtA0juPwtA@ifi.uio.no>
2007-02-28  0:20           ` Robert Hancock
2007-02-28  1:32             ` Hiro Yoshioka

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