Since commit 2f36825b1 ("sched: Next buddy hint on sleep and preempt
path") it is likely we pick a new task from the same cgroup, doing a put
and then set on all intermediate entities is a waste of time, so try to
avoid this.XXX please review carefully; its quite horrid. That said, simple hackbench runs in a 3 deep cgroup show a consistent performance increase (small, but consistent). Signed-off-by: Peter Zijlstra <pet...@infradead.org> Link: http://lkml.kernel.org/r/1328936700.2476.17.camel@laptop --- kernel/sched/fair.c | 140 +++++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 111 insertions(+), 29 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2738,15 +2738,46 @@ wakeup_preempt_entity(struct sched_entit */ static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq) { - struct sched_entity *se = __pick_first_entity(cfs_rq); - struct sched_entity *left = se; + struct sched_entity *left = __pick_first_entity(cfs_rq); + struct sched_entity *se, *curr = cfs_rq->curr; + + /* + * Since its possible we got here without doing put_prev_entity() we + * also have to consider cfs_rq->curr. If it was set, and is still a + * runnable entity, update_curr() will update its vruntime, otherwise + * forget we've ever seen it. + */ + if (curr) { + if (curr->on_rq) + update_curr(cfs_rq); + else + curr = NULL; + } + + /* + * If curr is set we have to see if its left of the leftmost entity + * still in the tree, provided there was anything in the tree at all. + */ + if (!left || (curr && entity_before(curr, left))) + left = curr; + + se = left; /* ideally we run the leftmost entity */ /* * Avoid running the skip buddy, if running something else can * be done without getting too unfair. */ if (cfs_rq->skip == se) { - struct sched_entity *second = __pick_next_entity(se); + struct sched_entity *second; + + if (se == curr) { + second = __pick_first_entity(cfs_rq); + } else { + second = __pick_next_entity(se); + if (!second || (curr && entity_before(curr, second))) + second = curr; + } + if (second && wakeup_preempt_entity(second, left) < 1) se = second; } @@ -2768,7 +2799,7 @@ static struct sched_entity *pick_next_en return se; } -static void check_cfs_rq_runtime(struct cfs_rq *cfs_rq); +static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq); static void put_prev_entity(struct cfs_rq *cfs_rq, struct sched_entity *prev) { @@ -3423,22 +3454,23 @@ static void check_enqueue_throttle(struc } /* conditionally throttle active cfs_rq's from put_prev_entity() */ -static void check_cfs_rq_runtime(struct cfs_rq *cfs_rq) +static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq) { if (!cfs_bandwidth_used()) - return; + return false; if (likely(!cfs_rq->runtime_enabled || cfs_rq->runtime_remaining > 0)) - return; + return false; /* * it's possible for a throttled entity to be forced into a running * state (e.g. set_curr_task), in this case we're finished. */ if (cfs_rq_throttled(cfs_rq)) - return; + return true; throttle_cfs_rq(cfs_rq); + return true; } static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer) @@ -3548,7 +3580,7 @@ static inline u64 cfs_rq_clock_task(stru } static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) {} -static void check_cfs_rq_runtime(struct cfs_rq *cfs_rq) {} +static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq) { return false; } static void check_enqueue_throttle(struct cfs_rq *cfs_rq) {} static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq) {} @@ -4484,44 +4516,94 @@ static void check_preempt_wakeup(struct set_last_buddy(se); } +/* + * Account for a descheduled task: + */ +static void put_prev_task_fair(struct rq *rq, struct task_struct *prev) +{ + struct sched_entity *se = &prev->se; + struct cfs_rq *cfs_rq; + + for_each_sched_entity(se) { + cfs_rq = cfs_rq_of(se); + put_prev_entity(cfs_rq, se); + } +} + static struct task_struct * pick_next_task_fair(struct rq *rq, struct task_struct *prev) { + struct sched_entity *se, __maybe_unused *pse; struct task_struct *p; - struct cfs_rq *cfs_rq = &rq->cfs; - struct sched_entity *se; + struct cfs_rq *cfs_rq; + +again: __maybe_unused + cfs_rq = &rq->cfs; + + if (prev) { + if (!IS_ENABLED(CONFIG_FAIR_GROUP_SCHED) || + (prev->sched_class != &fair_sched_class)) { + prev->sched_class->put_prev_task(rq, prev); + prev = NULL; + } + } if (!cfs_rq->nr_running) return NULL; - if (prev) - prev->sched_class->put_prev_task(rq, prev); - do { se = pick_next_entity(cfs_rq); - set_next_entity(cfs_rq, se); + if (!prev) + set_next_entity(cfs_rq, se); cfs_rq = group_cfs_rq(se); } while (cfs_rq); p = task_of(se); - if (hrtick_enabled(rq)) - hrtick_start_fair(rq, p); - return p; -} +#ifdef CONFIG_FAIR_GROUP_SCHED + /* + * If we haven't yet done put_prev_entity and the selected task is + * a different task than we started out with, try and touch the least + * amount of cfs_rq trees. + */ + if (prev) { + if (prev != p) { + pse = &prev->se; + + while (!(cfs_rq = is_same_group(se, pse))) { + int se_depth = se->depth; + int pse_depth = pse->depth; + + if (se_depth <= pse_depth) { + put_prev_entity(cfs_rq_of(pse), pse); + pse = parent_entity(pse); + } + if (se_depth >= pse_depth) { + set_next_entity(cfs_rq_of(se), se); + se = parent_entity(se); + } + } -/* - * Account for a descheduled task: - */ -static void put_prev_task_fair(struct rq *rq, struct task_struct *prev) -{ - struct sched_entity *se = &prev->se; - struct cfs_rq *cfs_rq; + put_prev_entity(cfs_rq, pse); + set_next_entity(cfs_rq, se); + } - for_each_sched_entity(se) { - cfs_rq = cfs_rq_of(se); - put_prev_entity(cfs_rq, se); + /* + * In case the common cfs_rq got throttled, just give up and + * put the stack and retry. + */ + if (unlikely(check_cfs_rq_runtime(cfs_rq))) { + put_prev_task_fair(rq, p); + prev = NULL; + goto again; + } } +#endif + + if (hrtick_enabled(rq)) + hrtick_start_fair(rq, p); + + return p; } /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
