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 <shaohua.li@intel.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 7b850cd..9703298 100644 (file)
--- 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);
 }