Re: Scheduler fairness problem on 2.6 series (Attn: Nick Piggin and others)

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

spaminos-ker@yahoo.com wrote:
> --- Peter Williams <pwil3058@bigpond.net.au> wrote:
> 
>>The mode in which the scheduler was being used had all priority fiddling 
>>(except promotion) turned off so the tasks should have been just round 
>>robinning with each other.  Also, the time outs are fairly rare (every 
>>few hours according to Nicolas's e-mail) and happen with several 
>>different schedulers (with ZAPHOD (the one being used by Nicolas) and 
>>Con's staircase schedulers having less problem than the vanilla 
>>scheduler) which is why I thought it might be something outside the 
>>scheduler.  Perhaps it's something outside the kernel?
>>
> 
> 
> I can add to this that this problem occured on a variety of systems, single CPU
> Pentium IIIs and 4s, Athlon, dual PIIIs ;
> the one thing in common is that everything works fine on all those machines
> with 2.4, but breaks with 2.5 (or redhat 2.4 kernel with some backported code).

I don't suppose you know what the backported code was?  If you could 
provide a patch of the backport it might provide some clues.

> When I do the tests, the only thing I switch is the kernel and reboot.
> 
> It's true that it could be something broken outside of the scheduling code
> (like the way IRQ events are handled maybe, or the way signals are delivered).
> 
> The one difference between the artificial test (from the original post) and the
> real life test I do now, is that the real test combines disks I/O, network I/O
> (TCP/IP and UDP) and several multithreaded processes.
> Where things are kind of bad is that I am far from saturating the machine (the
> load average is less than 2), but still some processes get those annoying
> timeouts.

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

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