linux-kernel - [PATCH 3/4] sched/psi: extract update

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Date:   Thu,  9 Mar 2023 18:07:55 +0100
From:   Domenico Cerasuolo <cerasuolodomenico@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, surenb@...gle.com, brauner@...nel.org,
        chris@...isdown.name, hannes@...xchg.org,
        Domenico Cerasuolo <cerasuolodomenico@...il.com>
Subject: [PATCH 3/4] sched/psi: extract update_triggers side effect

The update of rtpoll_total inside update_triggers can be moved out of
the function since changed_states has the same information as the
update_total flag used in the function. Besides the simplification of
the function, with the next patch it would become an unwanted side
effect needed only for PSI_POLL.

Suggested-by: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@...il.com>
---
 kernel/sched/psi.c | 20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index a3d0b5cf797a..476941c1cbea 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -433,7 +433,6 @@ static u64 window_update(struct psi_window *win, u64 now, u64 value)
 static u64 update_triggers(struct psi_group *group, u64 now)
 {
 	struct psi_trigger *t;
-	bool update_total = false;
 	u64 *total = group->total[PSI_POLL];
 
 	/*
@@ -456,14 +455,6 @@ static u64 update_triggers(struct psi_group *group, u64 now)
 		 * events without dropping any).
 		 */
 		if (new_stall) {
-			/*
-			 * Multiple triggers might be looking at the same state,
-			 * remember to update group->polling_total[] once we've
-			 * been through all of them. Also remember to extend the
-			 * polling time if we see new stall activity.
-			 */
-			update_total = true;
-
 			/* Calculate growth since last update */
 			growth = window_update(&t->win, now, total[t->state]);
 			if (!t->pending_event) {
@@ -484,11 +475,6 @@ static u64 update_triggers(struct psi_group *group, u64 now)
 		/* Reset threshold breach flag once event got generated */
 		t->pending_event = false;
 	}
-
-	if (update_total)
-		memcpy(group->rtpoll_total, total,
-				sizeof(group->rtpoll_total));
-
 	return now + group->rtpoll_min_period;
 }
 
@@ -686,8 +672,12 @@ static void psi_rtpoll_work(struct psi_group *group)
 		goto out;
 	}
 
-	if (now >= group->rtpoll_next_update)
+	if (now >= group->rtpoll_next_update) {
 		group->rtpoll_next_update = update_triggers(group, now);
+		if (changed_states & group->rtpoll_states)
+			memcpy(group->rtpoll_total, group->total[PSI_POLL],
+				   sizeof(group->rtpoll_total));
+	}
 
 	psi_schedule_rtpoll_work(group,
 		nsecs_to_jiffies(group->rtpoll_next_update - now) + 1,
-- 
2.34.1