On Mon, Jun 11, 2007 at 09:36:34AM +0200, Ingo Molnar wrote:

* Paul E. McKenney [off-list ref] wrote:

quoted

2.6.21.4-rt12 boots on 4-CPU Opteron and passes several hours of 
rcutorture.  However, if I simply do "modprobe rcutorture", the kernel 
threads do not spread across the CPUs as I would expect them to, even 
given CFS.  Instead, the readers all stack up on a single CPU, and I 
have to use the "taskset" command to spread them out manually.  Is 
there some config parameter I am missing out on?

hm, what affinity do they start out with? Could they all be pinned to 
CPU#0 by default?

They start off with affinity masks of 0xf on a 4-CPU system.  I would
expect them to load-balance across the four CPUs, but they stay all
on the same CPU until long after I lose patience (many minutes).

Since there are eight readers, I use the following commands:

	taskset -p 3 pid1
	taskset -p 3 pid2
	taskset -p 6 pid3
	taskset -p 6 pid4
	taskset -p c pid5
	taskset -p c pid6
	taskset -p 9 pid7
	taskset -p 9 pid8

where the "pidn" are all replaced by the pids of the torture readers.

Before I do this, the processes are all sharing a single CPU.  After I
do this, they are spread reasonably nicely over the CPUs.  I do need to
allow some migration in order to fully test the realtime RCU variants
in the various preemption scenarios.

							Thanx, Paul