sched/core: Improve CPU hotplug latency for rcu_expedited=1 case

The sched_cpu_deactivate()->synchronize_rcu_mult() is not taking
expedited path even though rcu_expedited is enabled. So split
the synchronize_rcu_mult() call into synchronize_sched() and
synchronize_rcu() to improve the hotplug latency.

Change-Id: Ic21fbf790e7ed2f314b4058a489cde7813897c1f
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>
Signed-off-by: Adam W. Willis <return.of.octobot@gmail.com>

kernel/sched/core.c

@@ -8060,7 +8060,11 @@ int sched_cpu_deactivate(unsigned int cpu)
 	 *
 	 * Do sync before park smpboot threads to take care the rcu boost case.
 	 */
-	synchronize_rcu_mult(call_rcu, call_rcu_sched);
+
+#ifdef CONFIG_PREEMPT
+	synchronize_sched();
+#endif
+	synchronize_rcu();
 
 #ifdef CONFIG_SCHED_SMT
 	/*