linux-kernel - [RFC 4/5] rcu: Use leaf_node_for_each_mask_possible_cpu() in force_qs

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Date:   Fri,  9 Dec 2016 16:48:26 +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 4/5] rcu: Use leaf_node_for_each_mask_possible_cpu() in force_qs_rnp()

->qsmask of an RCU leaf node is usually more sparse than the
corresponding cpu_possible_mask. So replace the
for_each_leaf_node_possible_cpu() in force_qs_rnp() with
leaf_node_for_each_mask_possible_cpu() to save several checks.

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 kernel/rcu/tree.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 5f6802b9ba5f..10162ac71dbe 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3014,6 +3014,7 @@ static void force_qs_rnp(struct rcu_state *rsp,
 			 bool *isidle, unsigned long *maxj)
 {
 	int cpu;
+	unsigned long bit;
 	unsigned long flags;
 	unsigned long mask;
 	struct rcu_node *rnp;
@@ -3047,13 +3048,11 @@ static void force_qs_rnp(struct rcu_state *rsp,
 				continue;
 			}
 		}
-		for_each_leaf_node_possible_cpu(rnp, cpu) {
-			unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
-			if ((rnp->qsmask & bit) != 0) {
-				if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
-					mask |= bit;
-			}
-		}
+
+		leaf_node_for_each_mask_possible_cpu(rnp, rnp->qsmask, bit, cpu)
+			if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
+				mask |= 1 << bit;
+
 		if (mask != 0) {
 			/* Idle/offline CPUs, report (releases rnp->lock. */
 			rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
-- 
2.10.2