linux-kernel - [PATCH 02/16] srcu: Rename srcu_might_be_idle() to srcu_should

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Message-ID: <20241112145159.23032-3-frederic@kernel.org>
Date: Tue, 12 Nov 2024 15:51:45 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Neeraj Upadhyay <neeraj.upadhyay@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	rcu <rcu@...r.kernel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	bpf@...r.kernel.org,
	Neeraj Upadhyay <Neeraj.Upadhyay@....com>,
	Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH 02/16] srcu: Rename srcu_might_be_idle() to srcu_should_expedite()

From: "Paul E. McKenney" <paulmck@...nel.org>

SRCU auto-expedites grace periods that follow a sufficiently long idle
period, and the srcu_might_be_idle() function is used to make this
decision.  However, the upcoming light-weight SRCU readers will not do
auto-expediting because doing so would cause the grace-period machinery
to invoke synchronize_rcu_expedited() twice, with IPIs all around.
However, software-engineering considerations force this determination
to remain in srcu_might_be_idle().

This commit therefore changes the name of srcu_might_be_idle() to
srcu_should_expedite(), thus moving from what it currently does to why
it does it, this latter being more future-proof.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: <bpf@...r.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/rcu/srcutree.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 78afaffd1b26..2fe0abade9c0 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -1139,7 +1139,8 @@ static void srcu_flip(struct srcu_struct *ssp)
 }
 
 /*
- * If SRCU is likely idle, return true, otherwise return false.
+ * If SRCU is likely idle, in other words, the next SRCU grace period
+ * should be expedited, return true, otherwise return false.
  *
  * Note that it is OK for several current from-idle requests for a new
  * grace period from idle to specify expediting because they will all end
@@ -1159,7 +1160,7 @@ static void srcu_flip(struct srcu_struct *ssp)
  * negligible when amortized over that time period, and the extra latency
  * of a needlessly non-expedited grace period is similarly negligible.
  */
-static bool srcu_might_be_idle(struct srcu_struct *ssp)
+static bool srcu_should_expedite(struct srcu_struct *ssp)
 {
 	unsigned long curseq;
 	unsigned long flags;
@@ -1469,14 +1470,15 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
  * Implementation of these memory-ordering guarantees is similar to
  * that of synchronize_rcu().
  *
- * If SRCU is likely idle, expedite the first request.  This semantic
- * was provided by Classic SRCU, and is relied upon by its users, so TREE
- * SRCU must also provide it.  Note that detecting idleness is heuristic
- * and subject to both false positives and negatives.
+ * If SRCU is likely idle as determined by srcu_should_expedite(),
+ * expedite the first request.  This semantic was provided by Classic SRCU,
+ * and is relied upon by its users, so TREE SRCU must also provide it.
+ * Note that detecting idleness is heuristic and subject to both false
+ * positives and negatives.
  */
 void synchronize_srcu(struct srcu_struct *ssp)
 {
-	if (srcu_might_be_idle(ssp) || rcu_gp_is_expedited())
+	if (srcu_should_expedite(ssp) || rcu_gp_is_expedited())
 		synchronize_srcu_expedited(ssp);
 	else
 		__synchronize_srcu(ssp, true);
-- 
2.46.0