linux-kernel - [PATCH 1/4] rcu: Don't check irq nesting from rcu idle entry/exit

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Date:	Mon, 28 Nov 2011 22:24:44 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Josh Triplett <josh@...htriplett.org>
Subject: [PATCH 1/4] rcu: Don't check irq nesting from rcu idle entry/exit

rcu_idle_enter() and rcu_idle_exit() don't need to check
the irq nesting as they are not called from irq.

Only check dyntick_nesting from rcu_irq_enter() and
rcu_irq_exit().

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Josh Triplett <josh@...htriplett.org>
---
 kernel/rcutree.c |   18 ++++++++----------
 1 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 28f8f92..c2aaadf 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -350,10 +350,6 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
  */
 static void rcu_idle_enter_common(struct rcu_dynticks *rdtp)
 {
-	if (rdtp->dynticks_nesting) {
-		trace_rcu_dyntick("--=", rdtp->dynticks_nesting);
-		return;
-	}
 	trace_rcu_dyntick("Start", rdtp->dynticks_nesting);
 	if (!idle_cpu(smp_processor_id())) {
 		WARN_ON_ONCE(1);	/* must be idle task! */
@@ -417,7 +413,10 @@ void rcu_irq_exit(void)
 	rdtp = &__get_cpu_var(rcu_dynticks);
 	rdtp->dynticks_nesting--;
 	WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
-	rcu_idle_enter_common(rdtp);
+	if (rdtp->dynticks_nesting)
+		trace_rcu_dyntick("--=", rdtp->dynticks_nesting);
+	else
+		rcu_idle_enter_common(rdtp);
 	local_irq_restore(flags);
 }
 
@@ -430,10 +429,6 @@ void rcu_irq_exit(void)
  */
 static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
 {
-	if (oldval) {
-		trace_rcu_dyntick("++=", rdtp->dynticks_nesting);
-		return;
-	}
 	smp_mb__before_atomic_inc();  /* Force ordering w/previous sojourn. */
 	atomic_inc(&rdtp->dynticks);
 	/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
@@ -503,7 +498,10 @@ void rcu_irq_enter(void)
 	oldval = rdtp->dynticks_nesting;
 	rdtp->dynticks_nesting++;
 	WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
-	rcu_idle_exit_common(rdtp, oldval);
+	if (oldval)
+		trace_rcu_dyntick("++=", rdtp->dynticks_nesting);
+	else
+		rcu_idle_exit_common(rdtp, oldval);
 	local_irq_restore(flags);
 }
 
-- 
1.7.5.4

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