linux-kernel - [PATCH RFC rcu 11/19] srcu: Move heuristics fields from srcu_struct to srcu

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Date:   Thu, 23 Mar 2023 17:19:30 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...a.com,
        rostedt@...dmis.org, hch@....de,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH RFC rcu 11/19] srcu: Move heuristics fields from srcu_struct to srcu_usage

This commit moves the ->srcu_size_jiffies, ->srcu_n_lock_retries,
and ->srcu_n_exp_nodelay fields from the srcu_struct structure to the
srcu_usage structure to reduce the size of the former in order to improve
cache locality.

Suggested-by: Christoph Hellwig <hch@....de>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 include/linux/srcutree.h |  6 +++---
 kernel/rcu/srcutree.c    | 18 +++++++++---------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 7458df6bbe00..82d07466da93 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -73,6 +73,9 @@ struct srcu_usage {
 	unsigned long srcu_gp_seq_needed_exp;	/* Furthest future exp GP. */
 	unsigned long srcu_gp_start;		/* Last GP start timestamp (jiffies) */
 	unsigned long srcu_last_gp_end;		/* Last GP end timestamp (ns) */
+	unsigned long srcu_size_jiffies;	/* Current contention-measurement interval. */
+	unsigned long srcu_n_lock_retries;	/* Contention events in current interval. */
+	unsigned long srcu_n_exp_nodelay;	/* # expedited no-delays in current GP phase. */
 };
 
 /*
@@ -80,9 +83,6 @@ struct srcu_usage {
  */
 struct srcu_struct {
 	unsigned int srcu_idx;			/* Current rdr array element. */
-	unsigned long srcu_size_jiffies;	/* Current contention-measurement interval. */
-	unsigned long srcu_n_lock_retries;	/* Contention events in current interval. */
-	unsigned long srcu_n_exp_nodelay;	/* # expedited no-delays in current GP phase. */
 	struct srcu_data __percpu *sda;		/* Per-CPU srcu_data array. */
 	bool sda_is_static;			/* May ->sda be passed to free_percpu()? */
 	unsigned long srcu_barrier_seq;		/* srcu_barrier seq #. */
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 6c1ac78b1cfc..3f389b3a25aa 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -348,11 +348,11 @@ static void spin_lock_irqsave_check_contention(struct srcu_struct *ssp)
 	if (!SRCU_SIZING_IS_CONTEND() || ssp->srcu_sup->srcu_size_state)
 		return;
 	j = jiffies;
-	if (ssp->srcu_size_jiffies != j) {
-		ssp->srcu_size_jiffies = j;
-		ssp->srcu_n_lock_retries = 0;
+	if (ssp->srcu_sup->srcu_size_jiffies != j) {
+		ssp->srcu_sup->srcu_size_jiffies = j;
+		ssp->srcu_sup->srcu_n_lock_retries = 0;
 	}
-	if (++ssp->srcu_n_lock_retries <= small_contention_lim)
+	if (++ssp->srcu_sup->srcu_n_lock_retries <= small_contention_lim)
 		return;
 	__srcu_transition_to_big(ssp);
 }
@@ -624,8 +624,8 @@ static unsigned long srcu_get_delay(struct srcu_struct *ssp)
 		if (time_after(j, gpstart))
 			jbase += j - gpstart;
 		if (!jbase) {
-			WRITE_ONCE(ssp->srcu_n_exp_nodelay, READ_ONCE(ssp->srcu_n_exp_nodelay) + 1);
-			if (READ_ONCE(ssp->srcu_n_exp_nodelay) > srcu_max_nodelay_phase)
+			WRITE_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay, READ_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay) + 1);
+			if (READ_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay) > srcu_max_nodelay_phase)
 				jbase = 1;
 		}
 	}
@@ -783,7 +783,7 @@ static void srcu_gp_start(struct srcu_struct *ssp)
 				       rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq));
 	spin_unlock_rcu_node(sdp);  /* Interrupts remain disabled. */
 	WRITE_ONCE(ssp->srcu_sup->srcu_gp_start, jiffies);
-	WRITE_ONCE(ssp->srcu_n_exp_nodelay, 0);
+	WRITE_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay, 0);
 	smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
 	rcu_seq_start(&ssp->srcu_sup->srcu_gp_seq);
 	state = rcu_seq_state(ssp->srcu_sup->srcu_gp_seq);
@@ -1647,7 +1647,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
 		srcu_flip(ssp);
 		spin_lock_irq_rcu_node(ssp->srcu_sup);
 		rcu_seq_set_state(&ssp->srcu_sup->srcu_gp_seq, SRCU_STATE_SCAN2);
-		ssp->srcu_n_exp_nodelay = 0;
+		ssp->srcu_sup->srcu_n_exp_nodelay = 0;
 		spin_unlock_irq_rcu_node(ssp->srcu_sup);
 	}
 
@@ -1662,7 +1662,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
 			mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex);
 			return; /* readers present, retry later. */
 		}
-		ssp->srcu_n_exp_nodelay = 0;
+		ssp->srcu_sup->srcu_n_exp_nodelay = 0;
 		srcu_gp_end(ssp);  /* Releases ->srcu_gp_mutex. */
 	}
 }
-- 
2.40.0.rc2