linux-kernel - [RFC 2/5] rcu: Use leaf_node_for_each_mask_possible

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Date:   Fri,  9 Dec 2016 16:48:24 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: [RFC 2/5] rcu: Use leaf_node_for_each_mask_possible_cpu() in RCU stall checking

Replace for_each_leaf_node_possible_cpu() loop with
leaf_node_for_each_mask_possible_cpu() loop to gain fewer checks in RCU
stall checking code.

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 kernel/rcu/tree.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b56e2dc31ba5..5f6802b9ba5f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1412,15 +1412,16 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
 static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
 {
 	int cpu;
-	unsigned long flags;
+	unsigned long flags, bit;
 	struct rcu_node *rnp;
 
 	rcu_for_each_leaf_node(rsp, rnp) {
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
-		for_each_leaf_node_possible_cpu(rnp, cpu)
-			if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
-				if (!trigger_single_cpu_backtrace(cpu))
-					dump_cpu_task(cpu);
+
+		leaf_node_for_each_mask_possible_cpu(rnp, rnp->qsmask, bit, cpu)
+			if (!trigger_single_cpu_backtrace(cpu))
+				dump_cpu_task(cpu);
+
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	}
 }
@@ -1455,6 +1456,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 {
 	int cpu;
 	long delta;
+	unsigned long bit;
 	unsigned long flags;
 	unsigned long gpa;
 	unsigned long j;
@@ -1490,13 +1492,12 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 	rcu_for_each_leaf_node(rsp, rnp) {
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
 		ndetected += rcu_print_task_stall(rnp);
-		if (rnp->qsmask != 0) {
-			for_each_leaf_node_possible_cpu(rnp, cpu)
-				if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
-					print_cpu_stall_info(rsp, cpu);
-					ndetected++;
-				}
+
+		leaf_node_for_each_mask_possible_cpu(rnp, rnp->qsmask, bit, cpu) {
+			print_cpu_stall_info(rsp, cpu);
+			ndetected++;
 		}
+
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	}
 
-- 
2.10.2