Messages in this thread | | | Date | Thu, 20 Aug 2009 02:10:25 +0200 (CEST) | From | Marton Balint <> | Subject | Re: CPU scheduler weirdness? |
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On Wed, 19 Aug 2009, Peter Zijlstra wrote:
> On Wed, 2009-08-19 at 14:34 +0200, Marton Balint wrote: >> >> On Wed, 19 Aug 2009, Peter Zijlstra wrote: >> >>> On Wed, 2009-08-19 at 14:01 +0200, Marton Balint wrote: >>>> 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. >>> >>> Only one remains here.. on a c2q running 2.6.31-rc6-tip >>> >>> Do you have a .config handy? >>> >> >> Yes it's in my original post: >> >> http://marc.info/?l=linux-kernel&m=125012584709800&w=2 > > Right you are,.. so I build a kernel with the cgroup scheduler in and > tested it on a dual-core opteron machine, but I can't seem to reproduce > this. > > Are you using cgroups in any way, or do you simply have it enabled in > your config?
No, it's just enabled. Actually the kernel is from the openSUSE build service:
http://download.opensuse.org/repositories/Kernel:/HEAD/openSUSE_11.1/x86_64/
But the problem is present for both the kernel-default kernel and the kernel-vanilla kernel which does not contain any suse-specific patches.
This evening I had a bit more time to test, and I've made a surprising discovery: I can only reproduce the bug if the kernel module of my TV tuner card is loaded. I have a Leadtek Winfast 2000 XP Expert TV card, it uses the cx8800 kernel module. It seems that the problem is somehow related to the infrared sensor of the TV card, because I recompiled the module with the 'case CX88_BOARD_WINFAST2000XP_EXPERT:' line removed from cx88-input.c and I couldn't reproduce the bug with the new kernel module.
Regards, Marton
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