| From 02da26ad5ed6ea8680e5d01f20661439611ed776 Mon Sep 17 00:00:00 2001 |
| From: Vincent Guittot <vincent.guittot@linaro.org> |
| Date: Thu, 27 May 2021 14:29:16 +0200 |
| Subject: sched/fair: Make sure to update tg contrib for blocked load |
| |
| From: Vincent Guittot <vincent.guittot@linaro.org> |
| |
| commit 02da26ad5ed6ea8680e5d01f20661439611ed776 upstream. |
| |
| During the update of fair blocked load (__update_blocked_fair()), we |
| update the contribution of the cfs in tg->load_avg if cfs_rq's pelt |
| has decayed. Nevertheless, the pelt values of a cfs_rq could have |
| been recently updated while propagating the change of a child. In this |
| case, cfs_rq's pelt will not decayed because it has already been |
| updated and we don't update tg->load_avg. |
| |
| __update_blocked_fair |
| ... |
| for_each_leaf_cfs_rq_safe: child cfs_rq |
| update cfs_rq_load_avg() for child cfs_rq |
| ... |
| update_load_avg(cfs_rq_of(se), se, 0) |
| ... |
| update cfs_rq_load_avg() for parent cfs_rq |
| -propagation of child's load makes parent cfs_rq->load_sum |
| becoming null |
| -UPDATE_TG is not set so it doesn't update parent |
| cfs_rq->tg_load_avg_contrib |
| .. |
| for_each_leaf_cfs_rq_safe: parent cfs_rq |
| update cfs_rq_load_avg() for parent cfs_rq |
| - nothing to do because parent cfs_rq has already been updated |
| recently so cfs_rq->tg_load_avg_contrib is not updated |
| ... |
| parent cfs_rq is decayed |
| list_del_leaf_cfs_rq parent cfs_rq |
| - but it still contibutes to tg->load_avg |
| |
| we must set UPDATE_TG flags when propagting pending load to the parent |
| |
| Fixes: 039ae8bcf7a5 ("sched/fair: Fix O(nr_cgroups) in the load balancing path") |
| Reported-by: Odin Ugedal <odin@uged.al> |
| Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> |
| Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> |
| Reviewed-by: Odin Ugedal <odin@uged.al> |
| Link: https://lkml.kernel.org/r/20210527122916.27683-3-vincent.guittot@linaro.org |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| kernel/sched/fair.c | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| --- a/kernel/sched/fair.c |
| +++ b/kernel/sched/fair.c |
| @@ -8005,7 +8005,7 @@ static bool __update_blocked_fair(struct |
| /* Propagate pending load changes to the parent, if any: */ |
| se = cfs_rq->tg->se[cpu]; |
| if (se && !skip_blocked_update(se)) |
| - update_load_avg(cfs_rq_of(se), se, 0); |
| + update_load_avg(cfs_rq_of(se), se, UPDATE_TG); |
| |
| /* |
| * There can be a lot of idle CPU cgroups. Don't let fully |