[patch 2/3] nohz: change signal tick dependency to wakeup CPUs of member tasks

[Marcelo Tosatti]

Rather than waking up all nohz_full CPUs on the system, only wakeup 
the target CPUs of member threads of the signal.

Reduces interruptions to nohz_full CPUs.

Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com>

Index: linux-2.6/kernel/time/tick-sched.c
===================================================================
--- linux-2.6.orig/kernel/time/tick-sched.c
+++ linux-2.6/kernel/time/tick-sched.c
@@ -446,7 +446,17 @@ EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_ta
  */
 void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits 
bit)
 {
-       tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
+       int prev;
+
+       prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask);
+       if (!prev) {
+               struct task_struct *t;
+
+               rcu_read_lock();
+               __for_each_thread(sig, t)
+                       tick_nohz_kick_task(t);
+               rcu_read_unlock();
+       }
 }
 
 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits 
bit)