Re: Strange thread behaviour on 8-way x86 machine

From: Mike Kravetz (
Date: Tue Jul 03 2001 - 13:51:39 EST

On Tue, Jul 03, 2001 at 12:25:12PM -0600, Sasha Pachev wrote:
> Hi,
> I have observed a rather strange behaviour doing a multi-threaded CPU
> benchmark on an 8-way machine running 2.4.2 SMP kernel. Even when the
> priority is reniced to the highest possible value, I am still unable to reach
> more than 50% CPU utilization. My benchmark just creates a bunch of threads
> with pthread_create(), and then runs a simple integer computation in each
> thread. On a dual with 2.4.3 kernel, and a 4-way with 2.4.2 kernel, I am able
> to reach full CPU utilization.

I haven't had any problem fully utilizing 8 CPUs on 2.4.* kernels. This
may seem obvious, but do you have more than 4 CPUs worth of work for the
system to do? What is the runqueue length during this benchmark?

Mike Kravetz                       
IBM Linux Technology Center
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