linux-kernel - [PATCH 2/6] Don't touch the snap in srcu_readers

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Date:	Tue, 6 Mar 2012 17:57:34 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org
Subject: [PATCH 2/6] Don't touch the snap in srcu_readers_active()

srcu_readers_active() is called without the mutex, but it touch the snap.
also achieve better cache locality a little

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
 kernel/srcu.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/kernel/srcu.c b/kernel/srcu.c
index b6b9ea2..fbe2d5f 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -181,7 +181,14 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
  */
 static int srcu_readers_active(struct srcu_struct *sp)
 {
-	return srcu_readers_active_idx(sp, 0) + srcu_readers_active_idx(sp, 1);
+	int cpu;
+	unsigned long sum = 0;
+
+	for_each_possible_cpu(cpu) {
+		sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]);
+		sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]);
+	}
+	return sum & SRCU_REF_MASK;
 }
 
 /**
-- 
1.7.4.4

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