Messages in this thread Patch in this message | | | Date | Fri, 29 Apr 2022 10:20:00 +0200 | From | Vincent Guittot <> | Subject | Re: [PATCH v7 2/7] sched/fair: Decay task PELT values during wakeup migration |
| |
Le vendredi 29 avril 2022 à 01:22:19 (+0800), Tao Zhou a écrit : > Hi Vincent, > > On Thu, Apr 28, 2022 at 03:38:39PM +0200, Vincent Guittot wrote: > > > On Wed, 27 Apr 2022 at 19:37, Tao Zhou <tao.zhou@linux.dev> wrote: > > >
[..]
> > > > + /* sync clock_pelt_idle with last update */ > > > > + if (cfs_rq->nr_running == 0) > > > > + update_idle_cfs_rq_clock_pelt(cfs_rq); > > > > > > I think that if cfs_rq->nr_running == 0 then use cfs rq pelt_idle to update > > > idle cfs rq. > > > > update_blocked_averages() updates all cfs rq to be aligned with now so > > we don't need to calculate an estimated now. update_rq_clock(rq) is > > called 1st to update the rq->clock and childs > > > > With only need to save when happened the last update which is done in > > update_rq_clock_pelt(rq) for rq->clock_pelt and with > > update_idle_cfs_rq_clock_pelt(cfs) for the cfs_rq_clock_pelt > > I missed this.
I ended up with something a bit different:
--- kernel/sched/fair.c | 133 ++++++++++++++++++++++++++++++++++--------- kernel/sched/pelt.h | 66 ++++++++++++++++++--- kernel/sched/sched.h | 10 ++++ 3 files changed, 174 insertions(+), 35 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index abd1feeec0c2..63e4cf225292 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3335,27 +3335,12 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq) if (cfs_rq->load.weight) return false; - if (cfs_rq->avg.load_sum) - return false; - - if (cfs_rq->avg.util_sum) - return false; - - if (cfs_rq->avg.runnable_sum) + if (load_avg_is_decayed(&cfs_rq->avg)) return false; if (child_cfs_rq_on_list(cfs_rq)) return false; - /* - * _avg must be null when _sum are null because _avg = _sum / divider - * Make sure that rounding and/or propagation of PELT values never - * break this. - */ - SCHED_WARN_ON(cfs_rq->avg.load_avg || - cfs_rq->avg.util_avg || - cfs_rq->avg.runnable_avg); - return true; } @@ -3694,6 +3679,88 @@ static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum #endif /* CONFIG_FAIR_GROUP_SCHED */ +#ifdef CONFIG_NO_HZ_COMMON +static inline void migrate_se_pelt_lag(struct sched_entity *se) +{ + struct cfs_rq *cfs_rq; + struct rq *rq; + bool is_idle; + u64 now, throttled = 0; + + /* utilization is already fully decayed */ + if (load_avg_is_decayed(&se->avg)) + return; + + cfs_rq = cfs_rq_of(se); + rq = rq_of(cfs_rq); + + rcu_read_lock(); + is_idle = is_idle_task(rcu_dereference(rq->curr)); + rcu_read_unlock(); + + /* + * The lag estimation comes with a cost we don't want to pay all the + * time. Hence, limiting to the case where the source CPU is idle and + * we know we are at the greatest risk to have an outdated clock. + */ + if (!is_idle) + return; + + /* + * Estimated "now" is: + * last_update_time: last update of the cfs_lock_pelt + + * cfs_idle_lag: rq_clock_pelt delta bewteen last cfs update and last rq update + + * rq_idle_lag: rq_clock delta between last rq update and now + * + * with + * + * last_update_time == cfs_clock_pelt() + * == rq_clock_pelt() - cfs->throttled_clock_pelt_time + * + * cfs_idle_lag: rq_clock_pelt() when rq is idle - rq_clock_pelt() when cfs is idle + * + * rq_idle_lag : sched_clock_cpu() - rq_clock() when rq is idle + * + * In fact, rq_clock_pelt() that is used for last_update_time and when + * cfs is idle are the same because their last update happens atthe + * same time. + * + * We can optimize "now" to be: + * rq_clock_pelt when rq is idle - cfs->throttled_clock_pelt_time when cfs is idle + + * sched_clock_cpu() - rq_clock() when rq is idle + * + * when rq is idle + * rq_clock_pelt() is saved in rq->clock_pelt_idle + * rq_clock() is saved in rq->enter idle + * + * when cfs is idle + * cfs->throttled_clock_pelt_time is saved in cfs_rq->throttled_pelt_idle + * + * When !CFS_BANDWIDTH, cfs->throttled_clock_pelt_time is null + */ + +#ifdef CONFIG_CFS_BANDWIDTH + throttled = u64_u32_load(cfs_rq->throttled_pelt_idle); + /* The clock has been stopped for throttling */ + if (throttled == U64_MAX) + return; +#endif + + now = u64_u32_load(rq->clock_pelt_idle); + now -= throttled; + + /* An update happened while computing lag */ + if (now < cfs_rq_last_update_time(cfs_rq)) + return; + + now += sched_clock_cpu(cpu_of(rq)) - u64_u32_load(rq->enter_idle); + + __update_load_avg_blocked_se(now, se); +} +#else +static void migrate_se_pelt_lag(struct sched_entity *se) {} +#endif + /** * update_cfs_rq_load_avg - update the cfs_rq's load/util averages * @now: current time, as per cfs_rq_clock_pelt() @@ -4429,6 +4496,9 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) */ if ((flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)) != DEQUEUE_SAVE) update_min_vruntime(cfs_rq); + + if (cfs_rq->nr_running == 0) + update_idle_cfs_rq_clock_pelt(cfs_rq); } /* @@ -6946,6 +7016,8 @@ static void detach_entity_cfs_rq(struct sched_entity *se); */ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) { + struct sched_entity *se = &p->se; + /* * As blocked tasks retain absolute vruntime the migration needs to * deal with this by subtracting the old and adding the new @@ -6953,7 +7025,6 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) * the task on the new runqueue. */ if (READ_ONCE(p->__state) == TASK_WAKING) { - struct sched_entity *se = &p->se; struct cfs_rq *cfs_rq = cfs_rq_of(se); se->vruntime -= u64_u32_load(cfs_rq->min_vruntime); @@ -6965,25 +7036,29 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) * rq->lock and can modify state directly. */ lockdep_assert_rq_held(task_rq(p)); - detach_entity_cfs_rq(&p->se); + detach_entity_cfs_rq(se); } else { + remove_entity_load_avg(se); + /* - * We are supposed to update the task to "current" time, then - * its up to date and ready to go to new CPU/cfs_rq. But we - * have difficulty in getting what current time is, so simply - * throw away the out-of-date time. This will result in the - * wakee task is less decayed, but giving the wakee more load - * sounds not bad. + * Here, the task's PELT values have been updated according to + * the current rq's clock. But if that clock hasn't been + * updated in a while, a substantial idle time will be missed, + * leading to an inflation after wake-up on the new rq. + * + * Estimate the missing time from the cfs_rq last_update_time + * and update sched_avg to improve the PELT continuity after + * migration. */ - remove_entity_load_avg(&p->se); + migrate_se_pelt_lag(se); } /* Tell new CPU we are migrated */ - p->se.avg.last_update_time = 0; + se->avg.last_update_time = 0; /* We have migrated, no longer consider this task hot */ - p->se.exec_start = 0; + se->exec_start = 0; update_scan_period(p, new_cpu); } @@ -8149,6 +8224,10 @@ static bool __update_blocked_fair(struct rq *rq, bool *done) if (update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq)) { update_tg_load_avg(cfs_rq); + /* sync clock_pelt_idle with last update */ + if (cfs_rq->nr_running == 0) + update_idle_cfs_rq_clock_pelt(cfs_rq); + if (cfs_rq == &rq->cfs) decayed = true; } diff --git a/kernel/sched/pelt.h b/kernel/sched/pelt.h index 4ff2ed4f8fa1..4143c6dc64dc 100644 --- a/kernel/sched/pelt.h +++ b/kernel/sched/pelt.h @@ -37,6 +37,29 @@ update_irq_load_avg(struct rq *rq, u64 running) } #endif +static inline bool load_avg_is_decayed(struct sched_avg *sa) +{ + if (sa->load_sum) + return false; + + if (sa->util_sum) + return false; + + if (sa->runnable_sum) + return false; + + /* + * _avg must be null when _sum are null because _avg = _sum / divider + * Make sure that rounding and/or propagation of PELT values never + * break this. + */ + SCHED_WARN_ON(sa->load_avg || + sa->util_avg || + sa->runnable_avg); + + return true; +} + #define PELT_MIN_DIVIDER (LOAD_AVG_MAX - 1024) static inline u32 get_pelt_divider(struct sched_avg *avg) @@ -61,6 +84,23 @@ static inline void cfs_se_util_change(struct sched_avg *avg) WRITE_ONCE(avg->util_est.enqueued, enqueued); } +static inline u64 rq_clock_pelt(struct rq *rq) +{ + lockdep_assert_rq_held(rq); + assert_clock_updated(rq); + + return rq->clock_pelt - rq->lost_idle_time; +} + +/* The rq is idle, we can sync to clock_task */ +static inline void _update_idle_rq_clock_pelt(struct rq *rq) +{ + rq->clock_pelt = rq_clock_task(rq); + + u64_u32_store(rq->enter_idle, rq_clock(rq)); + u64_u32_store(rq->clock_pelt_idle, rq_clock_pelt(rq)); +} + /* * The clock_pelt scales the time to reflect the effective amount of * computation done during the running delta time but then sync back to @@ -76,8 +116,7 @@ static inline void cfs_se_util_change(struct sched_avg *avg) static inline void update_rq_clock_pelt(struct rq *rq, s64 delta) { if (unlikely(is_idle_task(rq->curr))) { - /* The rq is idle, we can sync to clock_task */ - rq->clock_pelt = rq_clock_task(rq); + _update_idle_rq_clock_pelt(rq); return; } @@ -130,17 +169,26 @@ static inline void update_idle_rq_clock_pelt(struct rq *rq) */ if (util_sum >= divider) rq->lost_idle_time += rq_clock_task(rq) - rq->clock_pelt; + + _update_idle_rq_clock_pelt(rq); } -static inline u64 rq_clock_pelt(struct rq *rq) +#ifdef CONFIG_CFS_BANDWIDTH +static inline void update_idle_cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { - lockdep_assert_rq_held(rq); - assert_clock_updated(rq); - - return rq->clock_pelt - rq->lost_idle_time; + /* + * Make sure that pending update of rq->clock_pelt_idle and + * rq->enter_idle are visible during update_blocked_average() before + * updating cfs_rq->throttled_pelt_idle. + */ + smp_wmb(); + if (unlikely(cfs_rq->throttle_count)) + u64_u32_store(cfs_rq->throttled_pelt_idle, U64_MAX); + else + u64_u32_store(cfs_rq->throttled_pelt_idle, + cfs_rq->throttled_clock_pelt_time); } -#ifdef CONFIG_CFS_BANDWIDTH /* rq->task_clock normalized against any time this cfs_rq has spent throttled */ static inline u64 cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { @@ -150,6 +198,7 @@ static inline u64 cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) return rq_clock_pelt(rq_of(cfs_rq)) - cfs_rq->throttled_clock_pelt_time; } #else +static inline void update_idle_cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { } static inline u64 cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { return rq_clock_pelt(rq_of(cfs_rq)); @@ -204,6 +253,7 @@ update_rq_clock_pelt(struct rq *rq, s64 delta) { } static inline void update_idle_rq_clock_pelt(struct rq *rq) { } +static inline void update_idle_cfs_rq_clock_pelt(struct cfs_rq *cfs_rq) { } #endif diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index e2cf6e48b165..ea9365e1a24e 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -641,6 +641,10 @@ struct cfs_rq { int runtime_enabled; s64 runtime_remaining; + u64 throttled_pelt_idle; +#ifndef CONFIG_64BIT + u64 throttled_pelt_idle_copy; +#endif u64 throttled_clock; u64 throttled_clock_pelt; u64 throttled_clock_pelt_time; @@ -1013,6 +1017,12 @@ struct rq { u64 clock_task ____cacheline_aligned; u64 clock_pelt; unsigned long lost_idle_time; + u64 clock_pelt_idle; + u64 enter_idle; +#ifndef CONFIG_64BIT + u64 clock_pelt_idle_copy; + u64 enter_idle_copy; +#endif atomic_t nr_iowait; -- 2.17.1
| |