Messages in this thread | | | Subject | Re: [PATCH 2/4] sched/fair: Decay task PELT values during migration | From | Dietmar Eggemann <> | Date | Mon, 20 Dec 2021 12:26:23 +0100 |
| |
On 09.12.21 17:11, Vincent Donnefort wrote:
[...]
> @@ -6899,6 +6899,14 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) > > static void detach_entity_cfs_rq(struct sched_entity *se); > > +static u64 rq_clock_pelt_estimator(struct rq *rq) > +{ > + u64 pelt_lag = sched_clock_cpu(cpu_of(rq)) - > + u64_u32_load(rq->clock_pelt_lag); > + > + return cfs_rq_last_update_time(&rq->cfs) + pelt_lag;
Why do you use `avg.last_update_time` (lut) of the root cfs_rq here?
p's lut was just synced to cfs_rq_of(se)'s lut in
migrate_task_rq_fair() (1) -> remove_entity_load_avg() -> sync_entity_load_avg(se) (2)
[...]
> @@ -6924,26 +6934,29 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) > * In case of TASK_ON_RQ_MIGRATING we in fact hold the 'old' > * rq->lock and can modify state directly. > */ > - lockdep_assert_rq_held(task_rq(p)); > - detach_entity_cfs_rq(&p->se); > + lockdep_assert_rq_held(rq); > + 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 - * throw away the out-of-date time.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 PELT clock lag, and update sched_avg to ensure > + * PELT continuity after migration. > */ > - remove_entity_load_avg(&p->se); > + __update_load_avg_blocked_se(rq_clock_pelt_estimator(rq), se);
We do __update_load_avg_blocked_se() now twice for p, 1. in (2) and then in (1) again.
[...]
| |