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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
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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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