linux-kernel - [PATCH v2 3/4] sched/fair: Wait before decaying max_newidle_lb

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Message-Id: <20211015124654.18093-4-vincent.guittot@linaro.org>
Date:   Fri, 15 Oct 2021 14:46:53 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com
Cc:     Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v2 3/4] sched/fair: Wait before decaying max_newidle_lb_cost

Decay max_newidle_lb_cost only when it has not been updated for a while
and ensure to not decay a recently changed value.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 include/linux/sched/topology.h | 2 +-
 kernel/sched/fair.c            | 8 +++++---
 kernel/sched/topology.c        | 2 +-
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 8f0f778b7c91..9c8878f201ab 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -98,7 +98,7 @@ struct sched_domain {
 
 	/* idle_balance() stats */
 	u64 max_newidle_lb_cost;
-	unsigned long next_decay_max_lb_cost;
+	unsigned long last_decay_max_lb_cost;
 
 	u64 avg_scan_cost;		/* select_idle_sibling */
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6b8065b72847..2967d13737b7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10265,10 +10265,10 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
 		 * Decay the newidle max times here because this is a regular
 		 * visit to all the domains. Decay ~1% per second.
 		 */
-		if (time_after(jiffies, sd->next_decay_max_lb_cost)) {
+		if (time_after(jiffies, sd->last_decay_max_lb_cost + HZ)) {
 			sd->max_newidle_lb_cost =
 				(sd->max_newidle_lb_cost * 253) / 256;
-			sd->next_decay_max_lb_cost = jiffies + HZ;
+			sd->last_decay_max_lb_cost = jiffies;
 			need_decay = 1;
 		}
 		max_cost += sd->max_newidle_lb_cost;
@@ -10912,8 +10912,10 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 
 			t1 = sched_clock_cpu(this_cpu);
 			domain_cost = t1 - t0;
-			if (domain_cost > sd->max_newidle_lb_cost)
+			if (domain_cost > sd->max_newidle_lb_cost) {
 				sd->max_newidle_lb_cost = domain_cost;
+				sd->last_decay_max_lb_cost = jiffies;
+			}
 
 			curr_cost += domain_cost;
 			t0 = t1;
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index c56faae461d9..edd71649d579 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1572,7 +1572,7 @@ sd_init(struct sched_domain_topology_level *tl,
 		.last_balance		= jiffies,
 		.balance_interval	= sd_weight,
 		.max_newidle_lb_cost	= 0,
-		.next_decay_max_lb_cost	= jiffies,
+		.last_decay_max_lb_cost	= jiffies,
 		.child			= child,
 #ifdef CONFIG_SCHED_DEBUG
 		.name			= tl->name,
-- 
2.17.1