Messages in this thread | | | Date | Fri, 6 Jan 2023 12:28:26 +0100 | Subject | Re: [RFC PATCH v4 1/2] sched/fair: Introduce short duration task check | From | Dietmar Eggemann <> |
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On 06/01/2023 09:34, Chen Yu wrote: > Hi Dietmar, > thanks for reviewing the patch! > On 2023-01-05 at 12:33:16 +0100, Dietmar Eggemann wrote: >> On 16/12/2022 07:11, Chen Yu wrote: >> >> [...] >> >>> @@ -5995,6 +6005,18 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) >>> >>> static void set_next_buddy(struct sched_entity *se); >>> >>> +static inline void dur_avg_update(struct task_struct *p, bool task_sleep) >>> +{ >>> + u64 dur; >>> + >>> + if (!task_sleep) >>> + return; >>> + >>> + dur = p->se.sum_exec_runtime - p->se.prev_sum_exec_runtime_vol; >>> + p->se.prev_sum_exec_runtime_vol = p->se.sum_exec_runtime; >> >> Shouldn't se->prev_sum_exec_runtime_vol be set in enqueue_task_fair() >> and not in dequeue_task_fair()->dur_avg_update()? Otherwise `dur` will >> contain sleep time. >> > After the task p is dequeued, p's sum_exec_runtime will not be increased.
True.
> Unless task p is switched in again, p's sum_exec_runtime will continue to > increase. So dur should not include the sleep time, because we substract
Not sure I get this sentence? p's se->sum_exec_runtime will only increase if p is current, so running?
> between the sum_exec_runtime rather than rq->clock_task. Not sure if I understand > this correctly?
No, you're right. We're not dealing with time snapshots but rather with sum_exec_runtime snapshots. So the value will not change between dequeue and the next enqueue.
e ... enqueue_task_fair() d ... dequeue_task_fair() s ... set_next_entity() p ... put_prev_entity() u ... update_curr_fair()->update_curr()
p1:
---|---||--|--|---|--|--||--- d es u p s u pd
^ ^ | | (A) (B)
Same se->prev_sum_exec_runtime_vol value in (A) and (B).
> My original thought was that, record the average run time of every section: > Only consider that task voluntarily relinquishes the CPU. > For example, suppose on CPU1, task p1 and p2 run alternatively: > > --------------------> time > > | p1 runs 1ms | p2 preempt p1 | p1 switch in, runs 0.5ms and blocks | > ^ ^ ^ > |_____________| |_____________________________________| > ^ > | > p1 dequeued > > p1's duration in one section is (1 + 0.5)ms. Because if p2 does not > preempt p1, p1 can run 1.5ms. This reflects the nature of a task, > how long it wishes to run at most. > >> Like we do for se->prev_sum_exec_runtime in set_next_entity() but for >> one `set_next_entity()-put_prev_entity()` run section. >> >> AFAICS, you want to measure the exec_runtime sum over all run sections >> between enqueue and dequeue. > Yes, we tried to record the 'decayed' average exec_runtime for each section. > Say, task p runs for a ms , then p is dequeued and blocks for b ms, and then > runs for c ms, its average duration is 0.875 * a + 0.125 * c , which is > what update_avg() does.
OK.
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