Messages in this thread | | | Date | Fri, 6 Jan 2023 16:34:26 +0800 | From | Chen Yu <> | Subject | Re: [RFC PATCH v4 1/2] sched/fair: Introduce short duration task check |
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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. 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 between the sum_exec_runtime rather than rq->clock_task. Not sure if I understand this correctly?
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.
thanks, Chenyu
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