On 13 Sep 2022 19:38:17 +0530 Pavan Kondeti <quic_pkondeti@xxxxxxxxxxx>
> Hi
>
> The fact that psi_avgs_work()->collect_percpu_times()->get_recent_times()
> run from a kworker thread, PSI_NONIDLE condition would be observed as
> there is a RUNNING task. So we would always end up re-arming the work.
>
> If the work is re-armed from the psi_avgs_work() it self, the backing off
> logic in psi_task_change() (will be moved to psi_task_switch soon) can't
> help. The work is already scheduled. so we don't do anything there.
>
> Probably I am missing some thing here. Can you please clarify how we
> shut off re-arming the psi avg work?
Instead of open coding schedule_delayed_work() in bid to check if timer
hits the idle task (see delayed_work_timer_fn()), the idle task is tracked
in psi_task_switch() and checked by kworker to see if it preempted the idle
task.
Only for thoughts now.
Hillf
+++ b/kernel/sched/psi.c
@@ -412,6 +412,8 @@ static u64 update_averages(struct psi_gr
return avg_next_update;
}
+static DEFINE_PER_CPU(int, prev_task_is_idle);
+
static void psi_avgs_work(struct work_struct *work)
{
struct delayed_work *dwork;
@@ -439,7 +441,7 @@ static void psi_avgs_work(struct work_st
if (now >= group->avg_next_update)
group->avg_next_update = update_averages(group, now);
- if (nonidle) {
+ if (nonidle && 0 == per_cpu(prev_task_is_idle, raw_smp_processor_id())) {
schedule_delayed_work(dwork, nsecs_to_jiffies(
group->avg_next_update - now) + 1);
}
@@ -859,6 +861,7 @@ void psi_task_switch(struct task_struct
if (prev->pid) {
int clear = TSK_ONCPU, set = 0;
+ per_cpu(prev_task_is_idle, cpu) = 0;
/*
* When we're going to sleep, psi_dequeue() lets us
* handle TSK_RUNNING, TSK_MEMSTALL_RUNNING and
@@ -888,7 +891,8 @@ void psi_task_switch(struct task_struct
for (; group; group = iterate_groups(prev, &iter))
psi_group_change(group, cpu, clear, set, now, true);
}
- }
+ } else
+ per_cpu(prev_task_is_idle, cpu) = 1;
}
/**
