rcu: performance fixes to TINY_PREEMPT_RCU callback checking

This commit tightens up checks in rcu_preempt_check_callbacks() to avoid
unnecessary special handling at rcu_read_unlock() time.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
index c5bea1137dcb..6ceca4f745ff 100644
--- a/kernel/rcutiny_plugin.h
+++ b/kernel/rcutiny_plugin.h
@@ -72,7 +72,7 @@ static void rcu_report_exp_done(void);
 /*
  * Return true if the CPU has not yet responded to the current grace period.
  */
-static int rcu_cpu_cur_gp(void)
+static int rcu_cpu_blocking_cur_gp(void)
 {
         return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
 }
@@ -229,7 +229,7 @@ void rcu_preempt_note_context_switch(void)
                  * cannot end.
                  */
                 list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
-                if (rcu_cpu_cur_gp())
+                if (rcu_cpu_blocking_cur_gp())
                         rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
         }
 
@@ -368,12 +368,16 @@ static void rcu_preempt_check_callbacks(void)
 {
         struct task_struct *t = current;
 
-        if (!rcu_preempt_running_reader() && rcu_preempt_gp_in_progress())
+        if (rcu_preempt_gp_in_progress() &&
+            (!rcu_preempt_running_reader() ||
+             !rcu_cpu_blocking_cur_gp()))
                 rcu_preempt_cpu_qs();
         if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
             rcu_preempt_ctrlblk.rcb.donetail)
                 raise_softirq(RCU_SOFTIRQ);
-        if (rcu_preempt_gp_in_progress() && rcu_preempt_running_reader())
+        if (rcu_preempt_gp_in_progress() &&
+            rcu_cpu_blocking_cur_gp() &&
+            rcu_preempt_running_reader())
                 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
 }