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

[Peter Williams <pwil3058@bigpond.net.au>]

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