Re: CPU scheduler weirdness?

Marton Balint
2009-08-19T12:01:18Z

On Wed, 19 Aug 2009, Peter Zijlstra wrote:
> On Tue, 2009-08-18 at 21:49 +0200, Marton Balint wrote:
>
>> In the meantime, I was able to create a tiny C program which always
>> succesfully reproduces the bug. It's basically an endless loop which does
>> not stop while the process is running on the last CPU core. The program
>> creates multiple instances of itself, to be able to keep all of the CPU
>> cores busy. After 1 second, the processes running on other than the last
>> CPU core die, the processes running on the last CPU core remain stuck
>> there...
>>
>> I tested it on my dual core system, if someone could test it on a quad
>> core and report back that would probably be useful.
>>
>> Usage: ./schedtest <number of CPU cores>
>>
>> And don't forget to kill the stuck processes after using the program! :)
>
> So what's the bug? Sure one task will stay on the cpu, and because there
> is no contention it doesn't get migrated, and therefore won't quit,
> how's that a problem?

Problem is that more than one processes remain on that CPU core, and none
of them get migrated to other (idle) cores. I tested it with my E8400
processor and 2.6.31-rc5-git3 kernel.

Regards,
Marton