On Mon, Jun 11, 2007 at 09:36:34AM +0200, Ingo Molnar wrote:
>
> * Paul E. McKenney <[email protected]> wrote:
>
> > 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
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