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From: "Nish Aravamudan" <nish.aravamudan@gmail.com>
To: "Nick Piggin" <nickpiggin@yahoo.com.au>
Cc: "Rik van Riel" <riel@redhat.com>,
	"Lorenzo Allegrucci" <l_allegrucci@yahoo.it>,
	linux-kernel@vger.kernel.org, "Ingo Molnar" <mingo@elte.hu>,
	"Suparna Bhattacharya" <suparna@in.ibm.com>,
	"Jens Axboe" <jens.axboe@oracle.com>
Subject: Re: SMP performance degradation with sysbench
Date: Tue, 27 Feb 2007 17:27:07 -0800	[thread overview]
Message-ID: <29495f1d0702271727w358cc9o644c4017d50634a9@mail.gmail.com> (raw)
In-Reply-To: <45E2E244.8040009@yahoo.com.au>

[-- Attachment #1: Type: text/plain, Size: 2138 bytes --]

On 2/26/07, Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> Rik van Riel wrote:
> > Lorenzo Allegrucci wrote:
> >
> >> Hi lkml,
> >>
> >> according to the test below (sysbench) Linux seems to have scalability
> >> problems beyond 8 client threads:
> >> http://jeffr-tech.livejournal.com/6268.html#cutid1
> >> http://jeffr-tech.livejournal.com/5705.html
> >> Hardware is an 8-core amd64 system and jeffr seems willing to try more
> >> Linux versions on that machine.
> >> Anyway, is there anyone who can reproduce this?
> >
> >
> > I have reproduced it on a quad core test system.
> >
> > With 4 threads (on 4 cores) I get a high throughput, with
> > approximately 58% user time and 42% system time.
> >
> > With 8 threads (on 4 cores) I get way lower throughput,
> > with 37% user time, 29% system time 35% idle time!
> >
> > The maximum time taken per query also increases from
> > 0.0096s to 0.5273s. Ouch!
> >
> > I don't know if this is MySQL, glibc or Linux kernel,
> > but something strange is going on...
>
> Like you, I'm also seeing idle time start going up as threads increase.
>
> I initially thought this was a problem with the multiprocessor scheduler,
> because the pattern is exactly like some artificat in the load balancing.
>
> However, after looking at the stats, and testing a couple of things, I
> think it may not be after all.
>
> I've reproduced this on a 8-socket/16-way dual core Opteron. So far what
> I am seeing is that MySQL is having trouble putting enough load into the
> scheduler.

Here are some graphs from the 4-socket/8-way Xeon box (no SMT, no MC
in .config) I posted about earlier.

transactions.png resembles Nick's results pretty closely, in that a
drop-off occurs, at the same # of threads, too. That seems weird to
me, but I haven't thought about it too closely. Shouldn't Nick's be
dropping off closer to 16 threads (that would be 1 per core, then,
right?)

idle.png is the average % idle according to sar over each run from 1
to 32 threads. This appears to confirm what Rik was seeing.

Not sure if my data is hurting or helping, but this box remains
available for further tests.

Thanks,
Nish

[-- Attachment #2: transactions.png --]
[-- Type: image/png, Size: 3837 bytes --]

[-- Attachment #3: idle.png --]
[-- Type: image/png, Size: 3349 bytes --]

  parent reply	other threads:[~2007-02-28  1:27 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
2007-02-27 19:05                     ` Lorenzo Allegrucci
2007-03-01 16:57                       ` Lorenzo Allegrucci
2007-02-28  1:27     ` Nish Aravamudan [this message]
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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