On Mon, Jul 20, 2020 at 10:34:01AM +0200, Vincent Guittot wrote: > [ Upstream commit 01cfcde9c26d8555f0e6e9aea9d6049f87683998 ] > > task_h_load() can return 0 in some situations like running stress-ng > mmapfork, which forks thousands of threads, in a sched group on a 224 cores > system. The load balance doesn't handle this correctly because > env->imbalance never decreases and it will stop pulling tasks only after > reaching loop_max, which can be equal to the number of running tasks of > the cfs. Make sure that imbalance will be decreased by at least 1. > > We can't simply ensure that task_h_load() returns at least one because it > would imply to handle underflow in other places. > > Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > [removed misfit part which was not implemented yet] > Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx> > Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx> > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> > Tested-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> # v4.19 v4.14 v4.9 v4.4 > cc: Sasha Levin <sashal@xxxxxxxxxx> > Link: https://lkml.kernel.org/r/20200710152426.16981-1-vincent.guittot@xxxxxxxxxx > --- > > This patch also applies on v4.14.188 v4.9.230 and v4.4.230 Thanks for all of the backports, now queued up. greg k-h
