Re: 2.6.16-rc5-mm1 -- strange load balancing problems

Peter Williams
2006-03-02T22:23:45Z

Peter Williams wrote:
> I'm seeing some strange load balancing problems with this kernel. I
> don't think that they're due to the smpnice patches as I've applied them
> on a standard 2.6.15-rc5 kernel and the problem doesn't happen there.
>
> The problem is (as I say) quite strange and (for me) very reproducible.
> I have two programs (aspin and gsmiley) which I use to produce CPU hard
> spinners for testing purposes. What I'm finding is that when I start
> several copies of aspin load balancing goes as expected but when I
> launch several copies of gsmiley they all go to the one CPU and stick
> there like glue. (The most obvious difference between the two programs
> is that aspin is just a command line tool while gsmiley is an X windows
> program that spins a simley face and reports its own assessment of the
> percentage of CPU it's getting.) The machine that I've seen this
> problem is a hyper threading Pentium 4 and I suspect that it may be due
> to the SCHED_MC changes which overlap SCHED_SMT a bit.
>
> I'm trying to test this on a non hyper threading machine but the machine
> has crashed (different kernel) while doing the build. I'll resume this
> effort tomorrow but I thought that I should report the problem so that
> others could comment.
>
> Peter
> PS SCHED_MC was configured in but I'll try it without tomorrow and
> report the results.

Configuring SCHED_MC to "no" causes this problem to go away.

Peter
--
Peter Williams pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce