linux-kernel - Re: [PATCH linux-next] sched/psi: Avoid update triggers and rtpoll

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Message-ID: <202309141710195376952@zte.com.cn>
Date:   Thu, 14 Sep 2023 17:10:19 +0800 (CST)
From:   <yang.yang29@....com.cn>
To:     <surenb@...gle.com>
Cc:     <hannes@...xchg.org>, <mingo@...hat.com>,
        <linux-kernel@...r.kernel.org>, <juri.lelli@...hat.com>,
        <yang.yang29@....com.cn>
Subject: Re: [PATCH linux-next] sched/psi: Avoid update triggers and rtpoll_total when it is unnecessary

Update_total in update_triggers() is also only used by psi_rtpoll_work().
And when changed_states & group->rtpoll_states is true, update_total
should also be true, so try to delete update_total, please see below:

---
 kernel/sched/psi.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 81fca77397f6..744ba8b4e029 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -434,14 +434,13 @@ static u64 window_update(struct psi_window *win, u64 now, u64 value)
 	return growth;
 }

-static u64 update_triggers(struct psi_group *group, u64 now, bool *update_total,
+static void update_triggers(struct psi_group *group, u64 now,
 						   enum psi_aggregators aggregator)
 {
 	struct psi_trigger *t;
 	u64 *total = group->total[aggregator];
 	struct list_head *triggers;
 	u64 *aggregator_total;
-	*update_total = false;

 	if (aggregator == PSI_AVGS) {
 		triggers = &group->avg_triggers;
@@ -471,14 +470,6 @@ static u64 update_triggers(struct psi_group *group, u64 now, bool *update_total,
 		 * 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) {
@@ -499,8 +490,6 @@ static u64 update_triggers(struct psi_group *group, u64 now, bool *update_total,
 		/* Reset threshold breach flag once event got generated */
 		t->pending_event = false;
 	}
-
-	return now + group->rtpoll_min_period;
 }

 static u64 update_averages(struct psi_group *group, u64 now)
@@ -561,7 +550,6 @@ static void psi_avgs_work(struct work_struct *work)
 	struct delayed_work *dwork;
 	struct psi_group *group;
 	u32 changed_states;
-	bool update_total;
 	u64 now;

 	dwork = to_delayed_work(work);
@@ -580,7 +568,7 @@ static void psi_avgs_work(struct work_struct *work)
 	 * go - see calc_avgs() and missed_periods.
 	 */
 	if (now >= group->avg_next_update) {
-		update_triggers(group, now, &update_total, PSI_AVGS);
+		update_triggers(group, now, PSI_AVGS);
 		group->avg_next_update = update_averages(group, now);
 	}

@@ -636,7 +624,6 @@ static void psi_rtpoll_work(struct psi_group *group)
 {
 	bool force_reschedule = false;
 	u32 changed_states;
-	bool update_total;
 	u64 now;

 	mutex_lock(&group->rtpoll_trigger_lock);
@@ -702,10 +689,13 @@ static void psi_rtpoll_work(struct psi_group *group)
 	}

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

 	psi_schedule_rtpoll_work(group,
-- 
2.25.1