cpu: Wait for RCU grace periods concurrently
In kernels built with CONFIG_PREEMPT, _cpu_down() waits for RCU and
RCU-sched grace periods back-to-back, incurring quite a bit more latency
than required. This commit therefore uses the new synchronize_rcu_mult()
to allow waiting for both grace periods concurrently.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 9c9c9fa..d63b062 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -380,14 +380,14 @@
* will observe it.
*
* For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
- * not imply sync_sched(), so explicitly call both.
+ * not imply sync_sched(), so wait for both.
*
* Do sync before park smpboot threads to take care the rcu boost case.
*/
-#ifdef CONFIG_PREEMPT
- synchronize_sched();
-#endif
- synchronize_rcu();
+ if (IS_ENABLED(CONFIG_PREEMPT))
+ synchronize_rcu_mult(call_rcu, call_rcu_sched);
+ else
+ synchronize_rcu();
smpboot_park_threads(cpu);