On Thu, Nov 16, 2017 at 03:21:52PM +0100, Vincent Guittot wrote: > Unlike running, the runnable part can't be directly propagated through > the hierarchy when we migrate a task. The main reason is that runnable > time can be shared with other sched_entities that stay on the rq and > this runnable time will also remain on prev cfs_rq and must not be > removed. > > Instead, we can estimate what should be the new runnable of the prev > cfs_rq and check that this estimation stay in a possible range. The > prop_runnable_sum is a good estimation when adding runnable_sum but > fails most often when we remove it. Instead, we could use the formula > below instead: > > gcfs_rq's runnable_sum = gcfs_rq->avg.load_sum / gcfs_rq->load.weight > > which assumes that tasks are equally runnable which is not true but > easy to compute. > > Beside these estimates, we have several simple rules that help us to filter > out wrong ones: > > - ge->avg.runnable_sum <= than LOAD_AVG_MAX > - ge->avg.runnable_sum >= ge->avg.running_sum (ge->avg.util_sum << > LOAD_AVG_MAX) > - ge->avg.runnable_sum can't increase when we detach a task > > Cc: Yuyang Du <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Mike Galbraith <[email protected]> > Cc: Chris Mason <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Dietmar Eggemann <[email protected]> > Cc: Josef Bacik <[email protected]> > Cc: Ben Segall <[email protected]> > Cc: Paul Turner <[email protected]> > Cc: Tejun Heo <[email protected]> > Cc: Morten Rasmussen <[email protected]> > Signed-off-by: Vincent Guittot <[email protected]> > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > Link: http://lkml.kernel.org/r/[email protected]
Acked-by: Peter Zijlstra (Intel) <[email protected]> Ingo, can you stuff this in sched/urgent ?
