Messages in this thread | | | Date | Thu, 19 Jan 2023 22:29:01 +0800 | From | Chen Yu <> | Subject | Re: [RFC PATCH v4 1/2] sched/fair: Introduce short duration task check |
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Hi Peter, On 2023-01-16 at 11:33:26 +0100, Peter Zijlstra wrote: > On Thu, Jan 05, 2023 at 12:33:16PM +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. > > > > 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. > > You were thinking of the dynamic PELT window size thread? (which is what > I had to think of when I looked at this). > > I think we can still do that with this prev_sum_exec_runtime_vol (can't > say I love the name though). I agree that this name is not accurate, maybe prev_sleep_sum_exec_runtime? I'm open to any other name for this : )
Currently I'm checking Prateek's data on Zen3 and Yicong's data on Arm64, and their data suggested that: inhibiting the spreading of short wakee is not always a good idea on a system with small LLC. Meanwhile, according to my test on a system with large number of CPUs in 1 LLC, short duration wakee become a trouble maker if spreading them on different CPUs, which could trigger unexpected race condition. I'm thinking of taking nr_llc_cpu into consideration when defining a short duration task, and do some experiment on this.
thanks, Chenyu
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