Re: [Lse-tech] Re: CPU affinity & IPI latency

[Mike Kravetz]

On Sun, Jul 15, 2001 at 12:00:38PM -0500, Troy Benjegerdes wrote:
> 
> The next very interesting thing I found was that if I run something like 
> 'while true; do true; done' to load the other CPU while gzip is running, 
> gzip runs faster. The time change isn't very large, and appears to be just 
> barely detectable above the noise, but it definetly appears that gzip is 
> bouncing back and forth between cpus if both are idle.
> 
> I'm tempted to try the somewhat brute-force approach of increasing
> PROC_CHANGE_PENALTY, which is currently set to 20 (on ppc) to something
> like 100. Would this be an adequate 'short-term' solution util there is 
> some sort of multi-queue scheduler that everyone Linus likes? What are the 
> drawbacks of increasing PROC_CHANGE_PENALTY?

I'm pretty sure changing the value of PROC_CHANGE_PENALTY will not help
in this case.  PROC_CHANGE_PENALTY becomes increasingly important as
the number of running tasks is increased.  In the case of simply running
one task (like gzip) on your 2 CPU system, I don't think it will make
any difference.

-- 
Mike Kravetz                                 [e-mail]
IBM Linux Technology Center