Strange thread behaviour on 8-way x86 machine

From: Sasha Pachev (
Date: Tue Jul 03 2001 - 13:25:12 EST


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.

At first glance, it appears to be like some overzealous fairness problem in
the scheduler that is exhibited only when you have more than 4 CPUs. Before I
start scrutinizing the source trying to understand the inner workings of the
scheduler, I would like to get some feedback from people that know something
about the subject. Any ideas/suggestions would be appreciated.

MySQL Development Team
For technical support contracts, visit
   __  ___     ___ ____  __ 
  /  |/  /_ __/ __/ __ \/ /   Sasha Pachev <>
 / /|_/ / // /\ \/ /_/ / /__  MySQL AB,
/_/  /_/\_, /___/\___\_\___/  Provo, Utah, USA
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

This archive was generated by hypermail 2b29 : Sat Jul 07 2001 - 21:00:12 EST