From: Ingo Molnar <mingo@elte.hu>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jiri Kosina <jkosina@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Mike Galbraith <efault@gmx.de>,
David Miller <davem@davemloft.net>,
rjw@sisk.pl, s0mbre@tservice.net.ru,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [tbench regression fixes]: digging out smelly deadmen.
Date: Mon, 27 Oct 2008 19:33:12 +0100 [thread overview]
Message-ID: <20081027183312.GD11494@elte.hu> (raw)
In-Reply-To: <20081027113306.5b1d5898@lxorguk.ukuu.org.uk>
* Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> > The way to get the best possible dbench numbers in CPU-bound dbench
> > runs, you have to throw away the scheduler completely, and do this
> > instead:
> >
> > - first execute all requests of client 1
> > - then execute all requests of client 2
> > ....
> > - execute all requests of client N
>
> Rubbish. [...]
i've actually implemented that about a decade ago: i've tracked down
what makes dbench tick, i've implemented the kernel heuristics for it
to make dbench scale linearly with the number of clients - just to be
shot down by Linus about my utter rubbish approach ;-)
> [...] If you do that you'll not get enough I/O in parallel to
> schedule the disk well (not that most of our I/O schedulers are
> doing the job well, and the vm writeback threads then mess it up and
> the lack of Arjans ioprio fixes then totally screw you) </rant>
the best dbench results come from systems that have enough RAM to
cache the full working set, and a filesystem intelligent enough to not
insert bogus IO serialization cycles (ext3 is not such a filesystem).
The moment there's real IO it becomes harder to analyze but the same
basic behavior remains: the more unfair the IO scheduler, the "better"
dbench results we get.
Ingo
next prev parent reply other threads:[~2008-10-27 18:33 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-09 23:17 [tbench regression fixes]: digging out smelly deadmen Evgeniy Polyakov
2008-10-10 5:40 ` Peter Zijlstra
2008-10-10 8:09 ` Evgeniy Polyakov
2008-10-10 9:15 ` Ingo Molnar
2008-10-10 11:31 ` Evgeniy Polyakov
2008-10-10 11:40 ` Ingo Molnar
2008-10-10 13:25 ` Evgeniy Polyakov
2008-10-10 11:42 ` Ingo Molnar
2008-10-10 11:55 ` Evgeniy Polyakov
2008-10-10 11:57 ` Ingo Molnar
2008-10-24 22:25 ` Rafael J. Wysocki
2008-10-24 23:31 ` David Miller
2008-10-25 4:05 ` Mike Galbraith
2008-10-25 5:15 ` David Miller
2008-10-25 5:53 ` Mike Galbraith
2008-10-25 11:13 ` Rafael J. Wysocki
2008-10-26 3:55 ` David Miller
2008-10-26 11:33 ` Rafael J. Wysocki
2008-10-25 3:37 ` Mike Galbraith
2008-10-25 5:16 ` David Miller
2008-10-25 5:58 ` Mike Galbraith
2008-10-25 6:53 ` Mike Galbraith
2008-10-25 7:24 ` David Miller
2008-10-25 7:52 ` Mike Galbraith
2008-10-25 23:10 ` Jiri Kosina
2008-10-26 8:46 ` Mike Galbraith
2008-10-26 9:00 ` Peter Zijlstra
2008-10-26 9:11 ` Andrew Morton
2008-10-26 9:27 ` Evgeniy Polyakov
2008-10-26 9:34 ` Andrew Morton
2008-10-26 10:05 ` Evgeniy Polyakov
2008-10-27 2:34 ` David Miller
2008-10-27 9:30 ` Ingo Molnar
2008-10-27 9:57 ` David Miller
2008-10-26 10:23 ` Mike Galbraith
2008-10-26 19:03 ` Jiri Kosina
2008-10-27 9:29 ` Mike Galbraith
2008-10-27 10:42 ` Jiri Kosina
2008-10-27 11:27 ` Ingo Molnar
2008-10-27 11:33 ` Alan Cox
2008-10-27 12:06 ` Mike Galbraith
2008-10-27 13:42 ` Jiri Kosina
2008-10-27 14:17 ` Mike Galbraith
2008-10-27 18:33 ` Ingo Molnar [this message]
2008-10-27 19:39 ` Evgeniy Polyakov
2008-10-27 19:48 ` David Miller
2008-10-28 10:24 ` Mike Galbraith
2008-10-28 10:37 ` Ingo Molnar
2008-10-28 10:57 ` Mike Galbraith
2008-10-28 11:02 ` Ingo Molnar
2008-10-28 14:00 ` Mike Galbraith
2008-10-28 15:22 ` Mike Galbraith
2008-10-29 9:14 ` Evgeniy Polyakov
2008-10-29 9:50 ` Evgeniy Polyakov
2008-11-01 12:51 ` Paolo Ciarrocchi
2008-10-29 9:59 ` Nick Piggin
2008-10-26 9:15 ` Mike Galbraith
2008-10-25 7:19 ` David Miller
2008-10-25 7:33 ` Mike Galbraith
2008-10-27 17:26 ` Rick Jones
2008-10-27 19:11 ` Mike Galbraith
2008-10-27 19:18 ` Rick Jones
2008-10-27 19:44 ` Mike Galbraith
2008-10-26 11:29 ` Evgeniy Polyakov
2008-10-26 12:23 ` Evgeniy Polyakov
2008-10-30 18:15 ` Stephen Hemminger
2008-10-30 18:40 ` Evgeniy Polyakov
2008-10-30 18:43 ` Eric Dumazet
2008-10-30 18:56 ` Eric Dumazet
2008-10-30 19:01 ` Ilpo Järvinen
2008-10-31 7:52 ` David Miller
2008-10-31 9:40 ` Ilpo Järvinen
2008-10-31 9:51 ` David Miller
2008-10-31 10:42 ` Ilpo Järvinen
2008-10-31 10:45 ` Eric Dumazet
2008-10-31 11:01 ` Ilpo Järvinen
2008-10-31 11:10 ` Eric Dumazet
2008-10-31 11:15 ` Ilpo Järvinen
2008-10-31 19:57 ` Stephen Hemminger
2008-10-31 20:10 ` Evgeniy Polyakov
2008-10-31 21:03 ` Eric Dumazet
2008-10-31 21:18 ` Evgeniy Polyakov
2008-10-31 23:51 ` David Miller
2008-10-31 23:56 ` Stephen Hemminger
2008-11-01 0:16 ` Jay Vosburgh
2008-11-02 4:40 ` David Miller
2008-11-04 2:13 ` [PATCH net-next-2.6] bonding, net: Move last_rx update into bonding recv logic Jay Vosburgh
2008-11-04 2:17 ` David Miller
2008-10-10 10:13 ` [tbench regression fixes]: digging out smelly deadmen Mike Galbraith
2008-10-11 13:13 ` Evgeniy Polyakov
2008-10-11 14:39 ` Peter Zijlstra
2008-10-11 18:13 ` Mike Galbraith
2008-10-12 6:02 ` Mike Galbraith
2008-10-12 6:33 ` Mike Galbraith
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