[Devel] Re: [PATCH v3 5/6] Also record sleep start for a task group

[Peter Zijlstra]

On Wed, 2012-05-30 at 16:24 +0400, Glauber Costa wrote:
> sleep_start is not for iowait. This is for idle. And I know no other way 
> to collect idle time per cgroup, other than the time during which it was 
> out of the runqueue.
> 
> Now what you say about the sleepers don't make that much sense for idle 
> because this information is per-cpu as well.
> 
> When the se is being dequeued, it means none of its children is running 
> on that runqueue. That's idle. 

But does that mean the cgroup is idle? Its impossible to re-construct
the machine state from this per-cpu data if your definition of
cgroup-idle is the time when _all_ cpus are idle.