rcu: Avoid unnecessary self-wakeup of per-CPU kthreads

There are a number of cases where the RCU can find additional work for the per-CPU kthread within the context of that per-CPU kthread. In such cases, the per-CPU kthread is already running, so attempting to wake itself up does nothing except waste CPU cycles. This commit therefore checks to see if it is in the per-CPU kthread context, omitting the wakeup in this case. Signed-off-by: Shaohua Li <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]>
cbmeeks · Sep 29, 2011 · 1eb5212 · 1eb5212
1 parent 1f28809
commit 1eb5212
Showing 1 changed file with 3 additions and 5 deletions.
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
@@ -1291,11 +1291,9 @@ static void invoke_rcu_callbacks_kthread(void)
 
 	local_irq_save(flags);
 	__this_cpu_write(rcu_cpu_has_work, 1);
-	if (__this_cpu_read(rcu_cpu_kthread_task) == NULL) {
-		local_irq_restore(flags);
-		return;
-	}
-	wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
+	if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
+	    current != __this_cpu_read(rcu_cpu_kthread_task))
+		wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
 	local_irq_restore(flags);
 }