| Message ID | 20200720083401.22164-1-vincent.guittot@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [v4.19] sched/fair: handle case of task_h_load() returning 0 | expand |
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@linaro.org> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > [removed misfit part which was not implemented yet] > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > Cc: <stable@vger.kernel.org> # v4.19 v4.14 v4.9 v4.4 > cc: Sasha Levin <sashal@kernel.org> > Link: https://lkml.kernel.org/r/20200710152426.16981-1-vincent.guittot@linaro.org > --- > > 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
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 92b1e71f13c8..d8c249e6dcb7 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7337,7 +7337,15 @@ static int detach_tasks(struct lb_env *env) if (!can_migrate_task(p, env)) goto next; - load = task_h_load(p); + /* + * Depending of the number of CPUs and tasks and the + * cgroup hierarchy, task_h_load() can return a null + * value. Make sure that env->imbalance decreases + * otherwise detach_tasks() will stop only after + * detaching up to loop_max tasks. + */ + load = max_t(unsigned long, task_h_load(p), 1); + if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed) goto next;