[RFC v2 3/5] rcu: Use for_each_leaf_node_cpu() in ->expmask iteration

[Boqun Feng]

The ->expmask of an RCU leaf node should be more sparse than the
corresponding part of cpu_possible_mask, iterating over ->expmask bitmap
rather cpu_possible_mask to save some checks.

Signed-off-by: Boqun Feng <boqun.f...@gmail.com>
---
 kernel/rcu/tree_exp.h | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index a3a8756670d1..c4b3c8d01941 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -419,7 +419,6 @@ static void synchronize_sched_expedited_wait(struct 
rcu_state *rsp)
        int cpu;
        unsigned long jiffies_stall;
        unsigned long jiffies_start;
-       unsigned long mask;
        int ndetected;
        struct rcu_node *rnp;
        struct rcu_node *rnp_root = rcu_get_root(rsp);
@@ -444,12 +443,9 @@ static void synchronize_sched_expedited_wait(struct 
rcu_state *rsp)
                ndetected = 0;
                rcu_for_each_leaf_node(rsp, rnp) {
                        ndetected += rcu_print_task_exp_stall(rnp);
-                       for_each_leaf_node_possible_cpu(rnp, cpu) {
+                       for_each_leaf_node_cpu(rnp, rnp->expmask, cpu) {
                                struct rcu_data *rdp;
 
-                               mask = leaf_node_cpu_bit(rnp, cpu);
-                               if (!(rnp->expmask & mask))
-                                       continue;
                                ndetected++;
                                rdp = per_cpu_ptr(rsp->rda, cpu);
                                pr_cont(" %d-%c%c%c", cpu,
@@ -475,14 +471,10 @@ static void synchronize_sched_expedited_wait(struct 
rcu_state *rsp)
                        }
                        pr_cont("\n");
                }
-               rcu_for_each_leaf_node(rsp, rnp) {
-                       for_each_leaf_node_possible_cpu(rnp, cpu) {
-                               mask = leaf_node_cpu_bit(rnp, cpu);
-                               if (!(rnp->expmask & mask))
-                                       continue;
+               rcu_for_each_leaf_node(rsp, rnp)
+                       for_each_leaf_node_cpu(rnp, rnp->expmask, cpu)
                                dump_cpu_task(cpu);
-                       }
-               }
+
                jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
        }
 }
-- 
2.10.2