From: Antonio Flores Gil <aflo...@ditec.um.es>
Subject: Strange scheduling behavoir in SMP (kernel 2.2.14)
Date: 2000/01/27
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Hi,
I have a SMP machine with two Pentium III. In order to compare
performance with other machines I began a simple test:
for (i=0;i<MAX_NUMBER;i++)
for(j=0;j<MAX_NUMBER;j++)
c=a*b;
/* These variables could be integer or double */
Using kernel 2.2.12 with SMP support this simple program take more
time in my machine than in a uniprocessor with K6-2 (the same problem
appear in the last stable kernel 2.2.14) Using xosview
application I discovered where the problem was. Instead of staying
all the time in the same cpu, the process go from one cpu to other
with a big performance lost.
Am I right?. Has been this problem solved in 2.3.x series?
Thanks a lot in advance.
--
Prof. Antonio Flores Gil
Departamento de Ingeniería y Tecnología de Computadores. Facultad de
Informática. Universidad de Murcia
Campus de Espinardo - 30080 Murcia (SPAIN)
Tel.: +34-968-364638 Fax: +34-968-364151
email: aflo...@ditec.um.es
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From: Andrea Arcangeli <and...@suse.de>
Subject: Re: Strange scheduling behavoir in SMP (kernel 2.2.14)
Date: 2000/01/27
Message-ID: <fa.jigbd4v.1n06ggt@ifi.uio.no>#1/1
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To: Antonio Flores Gil <aflo...@ditec.um.es>
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On Wed, 26 Jan 2000, Antonio Flores Gil wrote:
>Using kernel 2.2.12 with SMP support this simple program take more time
in my machine than in a uniprocessor with K6-2 (the same problem appear
in the last stable kernel 2.2.14) Using xosview
>application I discovered where the problem was. Instead of staying all
the time in the same cpu, the process go from one cpu to other with a big performance lost.
>
>Am I right?. Has been this problem solved in 2.3.x series?
Very right. I fixed this quite some time ago. Run 2.2.14aa*latest or apply
this my patch on the top of 2.2.14 (or 2.2.12):
ftp://ftp.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.2/2.2.14aa3/SMP-scheduler-2.2.11-E.gz
I fixed this into the mid 2.3.x series (try out something like 2.3.17) but
FYI now the latest 2.3.4? are returned to not work correctly.
Andrea
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From: Peter Waltenberg <pet...@surf.dascom.com>
Subject: re: Strange scheduling behavoir in SMP (kernel 2.2.14)
Date: 2000/01/28
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> aflo...@ditec.um.es wrote
=============================
Hi,
I have a SMP machine with two Pentium III. In order to compare performance
with other machines I began a simple test:
for (i=0;i<MAX_NUMBER;i++)
for(j=0;j<MAX_NUMBER;j++)
c=a*b; /* These variables could be integer or double */
Using kernel 2.2.12 with SMP support this simple program take more time in my
machine than in a uniprocessor with K6-2 (the same problem appear in the last
stable kernel 2.2.14) Using xosview
application I discovered where the problem was. Instead of staying all the time
in the same cpu, the process go from one cpu to other with a big performance
lost.
Am I right?. Has been this problem solved in 2.3.x series?
Thanks a lot in advance.
===============================
No, it's still broken. Andrea has some patches for 2.2.
2.3 is still worse SMP than UP for anything CPU intensive.
I'm amazed that people are whinging about a phantom 5% in the scheduler when
there's a real 100%+ to be gained by fixing this one.
It's a real bug. The current scheduler kicks running processes even when
there's an idle CPU available. That means that heavy CPU use processes get
ping-ponged across CPU's.
It's bad on a Dual Celeron with small caches, it must be a real killer on an 8
way Xeon ;)
Peter
----------------------------------
Peter Waltenberg
Software Engineer
IBM Software Group, Gold Coast
Phone: +61 7 5578 8933
Fax: +61 7 5578 8146
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