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From: "Nish Aravamudan" <nish.aravamudan@gmail.com> To: "Paulo Marques" <pmarques@grupopie.com> Cc: "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: Tue, 27 Feb 2007 12:40:45 -0800 [thread overview] Message-ID: <29495f1d0702271240p1f446a74me9623ae756c67eb5@mail.gmail.com> (raw) In-Reply-To: <45E4469C.8000505@grupopie.com> On 2/27/07, Paulo Marques <pmarques@grupopie.com> 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. > > I don't know the scheduler code well enough, but comments like this one > make me think that the change is still in place: <snip> > If that is the case, turning off CONFIG_SCHED_SMT would solve the problem. To chime in here, I was attempting to reproduce this on an 8-way Xeon box (4 dual-core). SCHED_SMT and SCHED_MC on led to scaling issues when above 4 threads (4 threads was the peak). To the point, where I couldn't break 1000 transactions per second. Turning both off (with 2.6.20.1) gives much better performance through 16 threads. I am now running for the cases from 17 to 32 to see if I can reproduce the problem at hand. I'll regenerate my data and post numbers soon. I don't know if anyone else has those on in their kernel .config, but I'd suggest turning them off, as Paulo said. Thanks, Nish
next prev parent reply other threads:[~2007-02-27 20:40 UTC|newest] Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top 2007-02-25 17:44 SMP performance degradation with sysbench 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 [this message] 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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