[PATCH linux-next 2/3] sched/psi: Avoid update triggers and rtpoll_total when it is unnecessary

[yang.yang29]

From: Yang Yang <yang.yang29@xxxxxxxxxx>

When psimon wakes up and there are no state changes for rtpoll_states,
it's unnecessary to update triggers and rtpoll_total because the pressures
being monitored by user had not changed. This will help to slightly reduce
unnecessary computations of psi.

And update group->rtpoll_next_update after called update_triggers() and
update rtpoll_total. This will prevent bugs if update_triggers() uses
group->rtpoll_next_update in the future, and it makes more sense
to set the next update time after we finished the current update.

Signed-off-by: Yang Yang <yang.yang29@xxxxxxxxxx>
Suggested-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Suggested-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/sched/psi.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index be853f227e40..79f8db0c6150 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -704,11 +704,12 @@ static void psi_rtpoll_work(struct psi_group *group)
 	}

 	if (now >= group->rtpoll_next_update) {
-		update_triggers(group, now, &update_total, PSI_POLL);
-		group->rtpoll_next_update = now + group->rtpoll_min_period;
-		if (update_total)
+		if (changed_states & group->rtpoll_states) {
+			update_triggers(group, now, &update_total, PSI_POLL);
 			memcpy(group->rtpoll_total, group->total[PSI_POLL],
 				   sizeof(group->rtpoll_total));
+		}
+		group->rtpoll_next_update = now + group->rtpoll_min_period;
 	}

 	psi_schedule_rtpoll_work(group,
-- 
2.25.1