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

Peter Williams
2006-03-02T10:27:17Z

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

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