From 31bc6aeaab1d1de8959b67edbed5c7a4b3cdbe7c Mon Sep 17 00:00:00 2001 From: Vincent Guittot Date: Wed, 6 Feb 2019 17:14:21 +0100 Subject: [PATCH] sched/fair: Optimize update_blocked_averages() Removing a cfs_rq from rq->leaf_cfs_rq_list can break the parent/child ordering of the list when it will be added back. In order to remove an empty and fully decayed cfs_rq, we must remove its children too, so they will be added back in the right order next time. With a normal decay of PELT, a parent will be empty and fully decayed if all children are empty and fully decayed too. In such a case, we just have to ensure that the whole branch will be added when a new task is enqueued. This is default behavior since : commit f6783319737f ("sched/fair: Fix insertion in rq->leaf_cfs_rq_list") In case of throttling, the PELT of throttled cfs_rq will not be updated whereas the parent will. This breaks the assumption made above unless we remove the children of a cfs_rq that is throttled. Then, they will be added back when unthrottled and a sched_entity will be enqueued. As throttled cfs_rq are now removed from the list, we can remove the associated test in update_blocked_averages(). Signed-off-by: Vincent Guittot Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: sargun@sargun.me Cc: tj@kernel.org Cc: xiexiuqi@huawei.com Cc: xiezhipeng1@huawei.com Link: https://lkml.kernel.org/r/1549469662-13614-2-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 38d4669aa2ef..027f8e1b5b66 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -346,6 +346,18 @@ static inline bool list_add_leaf_cfs_rq(struct cfs_rq *cfs_rq) static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq) { if (cfs_rq->on_list) { + struct rq *rq = rq_of(cfs_rq); + + /* + * With cfs_rq being unthrottled/throttled during an enqueue, + * it can happen the tmp_alone_branch points the a leaf that + * we finally want to del. In this case, tmp_alone_branch moves + * to the prev element but it will point to rq->leaf_cfs_rq_list + * at the end of the enqueue. + */ + if (rq->tmp_alone_branch == &cfs_rq->leaf_cfs_rq_list) + rq->tmp_alone_branch = cfs_rq->leaf_cfs_rq_list.prev; + list_del_rcu(&cfs_rq->leaf_cfs_rq_list); cfs_rq->on_list = 0; } @@ -4438,6 +4450,10 @@ static int tg_unthrottle_up(struct task_group *tg, void *data) /* adjust cfs_rq_clock_task() */ cfs_rq->throttled_clock_task_time += rq_clock_task(rq) - cfs_rq->throttled_clock_task; + + /* Add cfs_rq with already running entity in the list */ + if (cfs_rq->nr_running >= 1) + list_add_leaf_cfs_rq(cfs_rq); } return 0; @@ -4449,8 +4465,10 @@ static int tg_throttle_down(struct task_group *tg, void *data) struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)]; /* group is entering throttled state, stop time */ - if (!cfs_rq->throttle_count) + if (!cfs_rq->throttle_count) { cfs_rq->throttled_clock_task = rq_clock_task(rq); + list_del_leaf_cfs_rq(cfs_rq); + } cfs_rq->throttle_count++; return 0; @@ -4553,6 +4571,8 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq) break; } + assert_list_leaf_cfs_rq(rq); + if (!se) add_nr_running(rq, task_delta); @@ -7700,10 +7720,6 @@ static void update_blocked_averages(int cpu) for_each_leaf_cfs_rq(rq, cfs_rq) { struct sched_entity *se; - /* throttled entities do not contribute to load */ - if (throttled_hierarchy(cfs_rq)) - continue; - if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq)) update_tg_load_avg(cfs_rq, 0);