Re: cgroups and SCHED_IDLE

[Holger Brunck <holger.brunck-SkAbAL50j+5BDgjK7y7TUQ@public.gmane.org>]

On 07/29/2013 04:07 PM, Peter Zijlstra wrote:
> On Mon, Jul 29, 2013 at 02:25:33PM +0200, Holger Brunck wrote:
>> On 07/23/2013 05:56 PM, Tejun Heo wrote:
>>>> On 06/27/2013 07:17 PM, Holger Brunck wrote:
>>>>
>>>> On a single ARM CPU (kirkwood) I see the same confusing results similar to the
>>>> results of the above powerpc example:
>>>>
>>>>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>>>>   232 root      20   0  1924  492  420 R 99.9  0.4   0:29.15 dd
>>>>   234 root      20   0  1924  492  420 R  0.3  0.4   0:00.13 dd
>>>>
>>>> I doublechecked this on my local host x86_64 multicore and here it works fine
>>>> even if I force both dd processes to run on the same CPU:
>>>>
>>>>   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>>>> 32046 root      20   0  102m  516  432 R 49.4  0.0   0:32.49 dd
>>>> 32049 root      20   0  102m  516  432 R 49.4  0.0   0:13.39 dd
>>>>
>>>> So either it's a problem for single CPUs or it's not allowed at all and works
>>>> only by chance.
>>>
>>> Can you please boot with maxcpus=1 and see whether that makes the
>>> issue reproducible on x86?
>>>
>>
>> I retested this with maxcpus=0 to disable SMP completely and it works, both
>> processes share 50% of the CPU. But I have to admit that I currently have only a
>> 3.4 setup for my x86_64 PC.
>>
>> My setup for an arm kirkwood board and a board with a powerpc 8247 runs latest
>> 3.10 kernel where I see the problem that one process is starving.  But the
>> problem was already present in a 3.0.x kernel. So it seems to be a architecture
>> dependent problem.
> 
> Does the below fix it?
> 

no, unfortunately I got the same results as before.

Two sched_idle task in the root group:

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  622 root      20   0  1924  492  420 R 49.8  0.4   0:20.26 dd
  623 root      20   0  1924  492  420 R 49.8  0.4   0:19.96 dd

After moving one of them into a subgroup:

[root@km_kirkwood /sys/fs/cgroup/cpu]# echo 623 > browser/tasks

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  623 root      20   0  1924  492  420 R 99.4  0.4   0:38.07 dd
  622 root      20   0  1924  492  420 R  0.3  0.4   0:30.15 dd

Regards
Holger