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From: "Nish Aravamudan" <nish.aravamudan@gmail.com>
To: "Bill Davidsen" <davidsen@tmr.com>
Cc: "Paulo Marques" <pmarques@grupopie.com>,
	"Rik van Riel" <riel@redhat.com>,
	"J.A. Magallón" <jamagallon@ono.com>,
	"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: Wed, 28 Feb 2007 16:20:54 -0800	[thread overview]
Message-ID: <29495f1d0702281620j43f576ack2d7e942136e8ea56@mail.gmail.com> (raw)
In-Reply-To: <29495f1d0702271852y5aab9d53mbd4b45931a393534@mail.gmail.com>

[-- Attachment #1: Type: text/plain, Size: 2012 bytes --]

On 2/27/07, Nish Aravamudan <nish.aravamudan@gmail.com> wrote:
> On 2/27/07, Bill Davidsen <davidsen@tmr.com> wrote:
> > Paulo Marques wrote:
> > > Rik van Riel wrote:
> > >> J.A. Magallón wrote:
> > >>> [...]
> > >>> 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.
> > >
> > > IIRC a long time ago there was a change in the scheduler to prevent a
> > > low prio task running on a sibling of a hyperthreaded processor to slow
> > > down a higher prio task on another sibling of the same processor.
> > >
> > > Basically the scheduler would put the low prio task to sleep during an
> > > adequate task slice to allow the other sibling to run at full speed for
> > > a while.
<snip>
> > > If that is the case, turning off CONFIG_SCHED_SMT would solve the problem.
<snip>
> > Note that Intel does make multicore HT processors, and hopefully when
> > this code works as intended it will result in more total throughput. My
> > supposition is that it currently is NOT working as intended, since
> > disabling SMT scheduling is reported to help.
>
> It does help, but we still drop off, clearly. Also, that's my
> baseline, so I'm not able to reproduce the *sharp* dropoff from the
> blog post yet.
>
> > A test with MC on and SMT off would be informative for where to look next.
>
> I'm rebooting my box with 2.6.20.1 and exactly this setup now.

Here are the results:

idle.png: average % idle over 120s runs from 1 to 32 threads
transactions.png: TPS over 120s runs from 1 to 32 threads

Hope the data is useful. All I can conclude right now is that SMT
appears to help (contradicting what I said earlier), but that MC seems
to have no effect (or no substantial effect).

Thanks,
Nish

[-- Attachment #2: idle.png --]
[-- Type: image/png, Size: 5482 bytes --]

[-- Attachment #3: transactions.png --]
[-- Type: image/png, Size: 6653 bytes --]

  reply	other threads:[~2007-03-01  0:20 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
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 [this message]
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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