Re: [PATCH v1 00/10] Optimize sched avgs computation and implement flat util hierarchy

[Yuyang Du]

On Tue, Aug 23, 2016 at 04:13:41PM +0200, Peter Zijlstra wrote:
> On Tue, Aug 23, 2016 at 03:28:19PM +0200, Vincent Guittot wrote:
> > I still wonder if using a flat util hierarchy is the right solution to
> > solve this problem with utilization and task group. I have noticed
> > exact same issues with load that generates weird task placement
> > decision and i think that we should probably try to solve both wrong
> > behavior with same mechanism. but this is not possible with flat
> > hierarchy for load
> > 
> > Let me take an example.
> > TA is a always running task on CPU1 in group /root/level1/
> > TB wakes up on CPU0 and moves TA into group /root/level2/
> > Even if TA stays on CPU1, runnable_load_avg of CPU1 root cfs rq will become 0.
> 
> Because while we migrate the load_avg on /root/level2, we do not
> propagate the load_avg up the hierarchy?
> 
> And always propagating everyrthing up will indeed also fix the
> utilization issue.

Yes, but for util it's actually irrespective to the number of
hirarchical levels, just propagating directly to the top cfs_rq
or simply rq will do. In other words, it's flat :)
 
> Of course, doing that propagation has its costs..
> 
> Didn't you post a patch doing just this a while ago?