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From: Paulo Marques <pmarques@grupopie.com>
To: Rik van Riel <riel@redhat.com>
Cc: "\"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: Tue, 27 Feb 2007 14:56:28 +0000	[thread overview]
Message-ID: <45E4469C.8000505@grupopie.com> (raw)
In-Reply-To: <45E439E4.5030703@redhat.com>

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.

I don't know the scheduler code well enough, but comments like this one 
make me think that the change is still in place:

> 	/*
> 	 * If an SMT sibling task has been put to sleep for priority
> 	 * reasons reschedule the idle task to see if it can now run.
> 	 */
> 	if (rq->nr_running) {
> 		resched_task(rq->idle);
> 		ret = 1;
> 	}

If that is the case, turning off CONFIG_SCHED_SMT would solve the problem.

-- 
Paulo Marques - www.grupopie.com

"The face of a child can say it all, especially the
mouth part of the face."

  reply	other threads:[~2007-02-27 14:56 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 [this message]
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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