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

[Yuyang Du]

On Tue, Aug 23, 2016 at 04:39:51PM +0100, Dietmar Eggemann wrote:
> On 23/08/16 15:45, Vincent Guittot wrote:
> > On 23 August 2016 at 16:13, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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?
> > 
> > yes. At now, the load of a cfs_rq and the load of its sched_entity
> > that represents it at parent level are disconnected
> 
> I guess you say 'disconnected' because cfs_rq and se (w/ cfs_rq eq.
> se->my_q) are now independent pelt signals where as before the rewrite
> they were 'connected' for load via __update_tg_runnable_avg(),
> __update_group_entity_contrib() in __update_entity_load_avg_contrib()
> and for utilization via 'se->avg.utilization_avg_contrib =
> group_cfs_rq(se)->utilization_load_avg' in
> __update_entity_utilization_avg_contrib().
 
I don't understand what exactly "disconnected" means, but with respect to
group_entity's load_avg, nothing is changed essentially:

group_entity_load_avg = my_cfs_rq_load_avg / tg_load_avg * tg_shares