Commit-ID: 67692435c411e5c53a1c588ecca2037aebd81f2e Gitweb: https://git.kernel.org/tip/67692435c411e5c53a1c588ecca2037aebd81f2e Author: Peter Zijlstra <pet...@infradead.org> AuthorDate: Wed, 29 May 2019 20:36:44 +0000 Committer: Peter Zijlstra <pet...@infradead.org> CommitDate: Thu, 8 Aug 2019 09:09:31 +0200
sched: Rework pick_next_task() slow-path Avoid the RETRY_TASK case in the pick_next_task() slow path. By doing the put_prev_task() early, we get the rt/deadline pull done, and by testing rq->nr_running we know if we need newidle_balance(). This then gives a stable state to pick a task from. Since the fast-path is fair only; it means the other classes will always have pick_next_task(.prev=NULL, .rf=NULL) and we can simplify. Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Aaron Lu <aaron....@gmail.com> Cc: Valentin Schneider <valentin.schnei...@arm.com> Cc: mi...@kernel.org Cc: Phil Auld <pa...@redhat.com> Cc: Julien Desfossez <jdesfos...@digitalocean.com> Cc: Nishanth Aravamudan <naravamu...@digitalocean.com> Link: https://lkml.kernel.org/r/aa34d24b36547139248f32a30138791ac6c02bd6.1559129225.git.vpil...@digitalocean.com --- kernel/sched/core.c | 19 ++++++++++++------- kernel/sched/deadline.c | 30 ++---------------------------- kernel/sched/fair.c | 9 ++++++--- kernel/sched/idle.c | 4 +++- kernel/sched/rt.c | 29 +---------------------------- kernel/sched/sched.h | 13 ++++++++----- kernel/sched/stop_task.c | 3 ++- 7 files changed, 34 insertions(+), 73 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 7bbe78a31ba5..a6661852907b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3791,7 +3791,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) p = fair_sched_class.pick_next_task(rq, prev, rf); if (unlikely(p == RETRY_TASK)) - goto again; + goto restart; /* Assumes fair_sched_class->next == idle_sched_class */ if (unlikely(!p)) @@ -3800,14 +3800,19 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) return p; } -again: +restart: + /* + * Ensure that we put DL/RT tasks before the pick loop, such that they + * can PULL higher prio tasks when we lower the RQ 'priority'. + */ + prev->sched_class->put_prev_task(rq, prev, rf); + if (!rq->nr_running) + newidle_balance(rq, rf); + for_each_class(class) { - p = class->pick_next_task(rq, prev, rf); - if (p) { - if (unlikely(p == RETRY_TASK)) - goto again; + p = class->pick_next_task(rq, NULL, NULL); + if (p) return p; - } } /* The idle class should always have a runnable task: */ diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 2872e15a87cd..0b9cbfb2b1d4 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1761,39 +1761,13 @@ pick_next_task_dl(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) struct task_struct *p; struct dl_rq *dl_rq; - dl_rq = &rq->dl; - - if (need_pull_dl_task(rq, prev)) { - /* - * This is OK, because current is on_cpu, which avoids it being - * picked for load-balance and preemption/IRQs are still - * disabled avoiding further scheduler activity on it and we're - * being very careful to re-start the picking loop. - */ - rq_unpin_lock(rq, rf); - pull_dl_task(rq); - rq_repin_lock(rq, rf); - /* - * pull_dl_task() can drop (and re-acquire) rq->lock; this - * means a stop task can slip in, in which case we need to - * re-start task selection. - */ - if (rq->stop && task_on_rq_queued(rq->stop)) - return RETRY_TASK; - } + WARN_ON_ONCE(prev || rf); - /* - * When prev is DL, we may throttle it in put_prev_task(). - * So, we update time before we check for dl_nr_running. - */ - if (prev->sched_class == &dl_sched_class) - update_curr_dl(rq); + dl_rq = &rq->dl; if (unlikely(!dl_rq->dl_nr_running)) return NULL; - put_prev_task(rq, prev); - dl_se = pick_next_dl_entity(rq, dl_rq); BUG_ON(!dl_se); diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 4418c1998e69..19c58599e967 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6770,7 +6770,7 @@ again: goto idle; #ifdef CONFIG_FAIR_GROUP_SCHED - if (prev->sched_class != &fair_sched_class) + if (!prev || prev->sched_class != &fair_sched_class) goto simple; /* @@ -6847,8 +6847,8 @@ again: goto done; simple: #endif - - put_prev_task(rq, prev); + if (prev) + put_prev_task(rq, prev); do { se = pick_next_entity(cfs_rq, NULL); @@ -6876,6 +6876,9 @@ done: __maybe_unused; return p; idle: + if (!rf) + return NULL; + new_tasks = newidle_balance(rq, rf); /* diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 8d59de2e4a6e..7c54550dda6a 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -389,7 +389,9 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf { struct task_struct *next = rq->idle; - put_prev_task(rq, prev); + if (prev) + put_prev_task(rq, prev); + set_next_task_idle(rq, next); return next; diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index dbdabd76f192..858c4cc6f99b 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -1553,38 +1553,11 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) struct task_struct *p; struct rt_rq *rt_rq = &rq->rt; - if (need_pull_rt_task(rq, prev)) { - /* - * This is OK, because current is on_cpu, which avoids it being - * picked for load-balance and preemption/IRQs are still - * disabled avoiding further scheduler activity on it and we're - * being very careful to re-start the picking loop. - */ - rq_unpin_lock(rq, rf); - pull_rt_task(rq); - rq_repin_lock(rq, rf); - /* - * pull_rt_task() can drop (and re-acquire) rq->lock; this - * means a dl or stop task can slip in, in which case we need - * to re-start task selection. - */ - if (unlikely((rq->stop && task_on_rq_queued(rq->stop)) || - rq->dl.dl_nr_running)) - return RETRY_TASK; - } - - /* - * We may dequeue prev's rt_rq in put_prev_task(). - * So, we update time before rt_queued check. - */ - if (prev->sched_class == &rt_sched_class) - update_curr_rt(rq); + WARN_ON_ONCE(prev || rf); if (!rt_rq->rt_queued) return NULL; - put_prev_task(rq, prev); - p = _pick_next_task_rt(rq); set_next_task_rt(rq, p); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index e085cffb8004..7111e3a1eeb4 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1700,12 +1700,15 @@ struct sched_class { void (*check_preempt_curr)(struct rq *rq, struct task_struct *p, int flags); /* - * It is the responsibility of the pick_next_task() method that will - * return the next task to call put_prev_task() on the @prev task or - * something equivalent. + * Both @prev and @rf are optional and may be NULL, in which case the + * caller must already have invoked put_prev_task(rq, prev, rf). * - * May return RETRY_TASK when it finds a higher prio class has runnable - * tasks. + * Otherwise it is the responsibility of the pick_next_task() to call + * put_prev_task() on the @prev task or something equivalent, IFF it + * returns a next task. + * + * In that case (@rf != NULL) it may return RETRY_TASK when it finds a + * higher prio class has runnable tasks. */ struct task_struct * (*pick_next_task)(struct rq *rq, struct task_struct *prev, diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c index 8f414018d5e0..7e1cee4e65b2 100644 --- a/kernel/sched/stop_task.c +++ b/kernel/sched/stop_task.c @@ -33,10 +33,11 @@ pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf { struct task_struct *stop = rq->stop; + WARN_ON_ONCE(prev || rf); + if (!stop || !task_on_rq_queued(stop)) return NULL; - put_prev_task(rq, prev); set_next_task_stop(rq, stop); return stop;
