From: "J . A . Magallon" <jamagallon@able.es>
To: "Albert D . Cahalan" <acahalan@cs.uml.edu>
Cc: Davide Libenzi <davidel@xmailserver.org>,
Christoph Hellwig <hch@ns.caldera.de>,
linux-kernel@vger.kernel.org, ognen@gene.pbi.nrc.ca
Subject: Re: threading question
Date: Wed, 13 Jun 2001 01:48:01 +0200 [thread overview]
Message-ID: <20010613014801.A17093@werewolf.able.es> (raw)
In-Reply-To: <XFMail.20010612144449.davidel@xmailserver.org> <200106122158.f5CLwTR253610@saturn.cs.uml.edu>
In-Reply-To: <200106122158.f5CLwTR253610@saturn.cs.uml.edu>; from acahalan@cs.uml.edu on Tue, Jun 12, 2001 at 23:58:29 +0200
On 20010612 Albert D. Cahalan wrote:
>
> In that case, this could be a hardware issue. Note that he seems
> to be comparing an x86 PC against SGI MIPS, Sun SPARC, and Compaq
> Alpha hardware.
>
> His data set is most likely huge. It's DNA data.
>
> The x86 box likely has small caches, a fast core, and a slow bus.
> So most of the time the CPU will be stalled waiting for a memory
> operation.
>
Perhaps is just synchronization of caches.
say you want to sum all the elements of a vector in parallele split in
two pieces:
int total=0;
thread 1:
for fist half
total += v[i]
thread 2:
for second half
total += v[i]
and you tought: 'well, I need a mutex for access to total. that will slow
down things, lets use separate counters':
int bigtotal;
int total[2];
thread 1:
for fist half
total[0] += v[i]
thread 2:
for second half
total[1] += v[i]
bigtotal = total[0]+total[1]
The problem ? total[0] and total[1] are nearby one of each other. So in
the same cache line. So on every write to total[?], even if they are
independent, system has to synchrnize caches.
Big iron (SGI, Sparc), has special hardware, but cheap PC mobos...
--
J.A. Magallon # Let the source be with you...
mailto:jamagallon@able.es
Linux Mandrake release 8.1 (Cooker) for i586
Linux werewolf 2.4.5-ac13 #1 SMP Sun Jun 10 21:42:28 CEST 2001 i686
next prev parent reply other threads:[~2001-06-12 23:59 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-06-12 18:24 threading question ognen
2001-06-12 18:39 ` Davide Libenzi
2001-06-12 18:57 ` from dmesg: kernel BUG at inode.c:486 Olivier Sessink
2001-06-12 18:58 ` threading question Christoph Hellwig
2001-06-12 19:07 ` ognen
2001-06-12 19:15 ` Kip Macy
2001-06-12 19:29 ` Christoph Hellwig
2001-06-12 19:15 ` Christoph Hellwig
2001-06-13 12:20 ` Kurt Garloff
2001-06-13 13:35 ` J . A . Magallon
2001-06-13 14:17 ` Philips
2001-06-13 15:06 ` ognen
2001-06-12 21:44 ` Davide Libenzi
2001-06-12 21:48 ` ognen
2001-06-14 18:15 ` Alan Cox
2001-06-14 22:42 ` threading question (results after thread pooling) ognen
2001-06-14 23:00 ` Mike Castle
2001-06-12 21:58 ` threading question Albert D. Cahalan
2001-06-12 23:48 ` J . A . Magallon [this message]
2001-06-12 19:06 ` Kip Macy
2001-06-12 19:14 ` Alexander Viro
2001-06-12 19:25 ` Russell Leighton
2001-06-12 23:27 ` Mike Castle
2001-06-13 17:31 ` bert hubert
2001-06-14 6:45 ` Helge Hafting
2001-06-14 18:28 ` Alan Cox
2001-06-14 19:01 ` bert hubert
2001-06-14 19:22 ` Russell Leighton
2001-06-15 11:29 ` Anil Kumar
2001-06-14 23:05 ` J . A . Magallon
2001-06-16 14:16 ` Michael Rothwell
2001-06-16 15:19 ` Alan Cox
2001-06-16 18:33 ` Russell Leighton
2001-06-16 19:06 ` Michael Rothwell
2001-06-16 21:30 ` Coroutines [was Re: threading question] Russell Leighton
2001-06-12 22:41 ` threading question Pavel Machek
2001-06-13 19:05 Hubertus Franke
[not found] <fa.f6da6av.agod3u@ifi.uio.no>
[not found] ` <fa.e54jbkv.kg4r99@ifi.uio.no>
2001-06-16 22:22 ` Dan Maas
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