On Mon, Oct 09, 2017 at 05:29:04PM +0200, Vincent Guittot wrote: > On 9 October 2017 at 17:03, Vincent Guittot <vincent.guit...@linaro.org> > wrote: > > On 1 September 2017 at 15:21, Peter Zijlstra <pet...@infradead.org> wrote:
> >> +/* > >> + * When on migration a sched_entity joins/leaves the PELT hierarchy, we > >> need to > >> + * propagate its contribution. The key to this propagation is the > >> invariant > >> + * that for each group: > >> + * > >> + * ge->avg == grq->avg (1) > >> + * > >> + * _IFF_ we look at the pure running and runnable sums. Because they > >> + * represent the very same entity, just at different points in the > >> hierarchy. > > > > I agree for the running part because only one entity can be running > > but i'm not sure for the pure runnable sum because we can have > > several runnable task in a cfs_rq but only one runnable group entity > > to reflect them or I misunderstand (1) The idea is that they (ge and grq) are the _same_ entity, just at different levels in the hierarchy. If the grq is runnable, it is through the ge. As a whole, they don't care how many runnable tasks there are. > > As an example, we have 2 always running task TA and TB so their > > load_sum is LOAD_AVG_MAX for each task The grq->avg.load_sum = \Sum > > se->avg.load_sum = 2*LOAD_AVG_MAX But the ge->avg.load_sum will be > > only LOAD_AVG_MAX > > > > So If we apply directly the d(TB->avg.load_sum) on the group hierachy > > and on ge->avg.load_sum in particular, the latter decreases to 0 > > whereas it should decrease only by half > > > > I have been able to see this wrong behavior with a rt-app json file > > > > so I think that we should instead remove only > > > > delta = se->avg.load_sum / grq->avg.load_sum * ge->avg.load_sum > > delta = se->avg.load_sum / (grq->avg.load_sum+se->avg.load_sum) * > ge->avg.load_sum > > as the se has already been detached > > > We don't have grq->avg.load_sum but we can have a rough estimate with > > grq->avg.load_avg/grq->weight Hurm, I think I see what you're saying, let me ponder this more.
