Re: SMP performance

Hi Igor,

Um, hmmm..where to begin?

First, SMP performance, good or bad, is almost certainly a function of
the kernel and is not a Gentoo specific problem.  

Second, I'm not aware of any SMP performance problems in recent 2.4.x
kernels.  

Particularly where we are speaking of 2 CPUs boxes.  2 CPU boxes offer
the most scalable SMP performance, in terms of being closest to the
theoretical limit.  Although I've not tried it, 4 way is reportedly
still quite scalable on 2.4 kernels, but beyond that, you reach the
point of diminishing returns.  As the 2.5 devlopment continues and the
BKL (Big Kernel Lock) is further eliminated, Linux will scale better and
better on larger SMP boxes, 8 CPUs and beyond.

If you can cite examples of SMP scaling problems, I (and probably others
on the list) would be interested in seeing them.

One last thought comes to mind:  If the tasks you speak of are I/O
bound, and (for example) do lots of sequential disk reads, but each task
reads different parts of the disk, then any SMP gains you may have
benefitted from by running tasks concurrently will surely be wiped out
due to latency of disk head seek times.  In this case, running the
processes sequentially would almost certainly be the winner.  But, that
doesn't say anything about SMP scalability of the Linux kernel.  It
tells you something about the seek and access times of your hard drive. 
-Mark

On Tue, 2002-09-03 at 20:42, Igor Schein wrote:
> Hi,
> 
> I was wondering if something is gonna be done about poor SMP
> performance in Gentoo.  I believe it a well known problem in SMP
> kernel, that if you run 2 simultaneous jobs on a 2-way machine, each
> job runs much slower then if they were run in sequence.   
> 
> Thanks
> 
> Igor
> _______________________________________________
> gentoo-newbies mailing list
> [email protected]
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> 
-- 
--
Mark J. Bobak
Oracle DBA
[email protected]
"It is not enough to have a good mind.  The main thing is to use it
well."
 						-- Rene Descartes