From: Vincent Guittot vincent.guittot@linaro.org
[ Upstream commit 5ab297bab984310267734dfbcc8104566658ebef ]
Even when a cgroup is throttled, the group se of a child cgroup can still be enqueued and its gse->on_rq stays true. When a task is enqueued on such child, we still have to update the load_avg and increase h_nr_running of the throttled cfs. Nevertheless, the 1st for_each_sched_entity() loop is skipped because of gse->on_rq == true and the 2nd loop because the cfs is throttled whereas we have to update both load_avg with the old h_nr_running and increase h_nr_running in such case.
The same sequence can happen during dequeue when se moves to parent before breaking in the 1st loop.
Note that the update of load_avg will effectively happen only once in order to sync up to the throttled time. Next call for updating load_avg will stop early because the clock stays unchanged.
Signed-off-by: Vincent Guittot vincent.guittot@linaro.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Fixes: 6d4d22468dae ("sched/fair: Reorder enqueue/dequeue_task_fair path") Link: https://lkml.kernel.org/r/20200306084208.12583-1-vincent.guittot@linaro.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/fair.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a486bf3d5078..7cd86641b44b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5289,15 +5289,15 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) for_each_sched_entity(se) { cfs_rq = cfs_rq_of(se);
- /* end evaluation on encountering a throttled cfs_rq */ - if (cfs_rq_throttled(cfs_rq)) - goto enqueue_throttle; - update_load_avg(cfs_rq, se, UPDATE_TG); update_cfs_group(se);
cfs_rq->h_nr_running++; cfs_rq->idle_h_nr_running += idle_h_nr_running; + + /* end evaluation on encountering a throttled cfs_rq */ + if (cfs_rq_throttled(cfs_rq)) + goto enqueue_throttle; }
enqueue_throttle: @@ -5386,15 +5386,16 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) for_each_sched_entity(se) { cfs_rq = cfs_rq_of(se);
- /* end evaluation on encountering a throttled cfs_rq */ - if (cfs_rq_throttled(cfs_rq)) - goto dequeue_throttle; - update_load_avg(cfs_rq, se, UPDATE_TG); update_cfs_group(se);
cfs_rq->h_nr_running--; cfs_rq->idle_h_nr_running -= idle_h_nr_running; + + /* end evaluation on encountering a throttled cfs_rq */ + if (cfs_rq_throttled(cfs_rq)) + goto dequeue_throttle; + }
dequeue_throttle: