Messages in this thread | | | Date | Mon, 21 Mar 2022 18:23:37 +0100 | Subject | Re: [PATCH v3 2/7] sched/fair: Decay task PELT values during migration | From | Dietmar Eggemann <> |
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On 08/03/2022 19:19, Vincent Donnefort wrote:
Patch header:
s/during migration/during wakeup migration ?
To make sure it's not related to lb migration (TASK_ON_RQ_MIGRATING).
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> Neither clock_task, clock_pelt nor clock can be accessed without the > runqueue lock. The new cfs_rq last_update_lag is therefore created and > encode those three values when the last_update_time value for that very
s/encode/encodes ... It's not really encoding?
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> Now we have an estimation for A + B, we can create an estimator for the > PELT value at the time of the migration. We need for this purpose to > inject last_update_time which is a combination of both clock_pelt and > lost_idle_time. The latter is a time value which is completely lost form a
s/form/from
> PELT point of view and must be ignored. And finally, we can write: > > rq_clock_pelt_estimator() = last_update_time + A + B > = last_update_time + > sched_clock_cpu() - last_update_lag
rq_clock_pelt_estimator() did exist in v2 but does not in v3 anymore. Might be misleading when people search for it.
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> @@ -3688,6 +3704,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq) > cfs_rq->last_update_time_copy, > sa->last_update_time); > #endif > + update_cfs_rq_lag(cfs_rq); > > return decayed; > } > @@ -6852,6 +6869,44 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) > > static void detach_entity_cfs_rq(struct sched_entity *se); > > +#ifdef CONFIG_NO_HZ_COMMON
Couldn't you put update_cfs_rq_lag() and migrate_se_pelt_lag() under one CONFIG_NO_HZ_COMMON?
> +static inline void migrate_se_pelt_lag(struct sched_entity *se)
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> + /* > + * 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 + * we know we are at the greatest risk to have an outdated clock.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; > + > + last_update_lag = u64_u32_load(cfs_rq->last_update_lag);
So each taskgroup has its own last_update_lag. I guess it works since we sync se in migrate_task_rq_fair() -> remove_entity_load_avg() -> sync_entity_load_avg() with its cfs_rq.
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> @@ -6859,6 +6914,9 @@ 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; > + struct cfs_rq *cfs_rq = cfs_rq_of(se);
This line can stay in the if condition below since cfs_rq is only used there. The brackets are also still there (A).
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> @@ -6866,8 +6924,6 @@ 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; <--- (A) > - struct cfs_rq *cfs_rq = cfs_rq_of(se);
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