[PATCH tip/core/rcu 01/16] rcu: Make expedited RCU-sched grace period immediately detect idle

[Paul E. McKenney]

Currently, sync_sched_exp_handler() will force a reschedule unless
this CPU has already checked in or unless a reschedule has already
been called for.  This is clearly wasteful if sync_sched_exp_handler()
interrupted an idle CPU, so this commit immediately reports the
quiescent state in that case.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 kernel/rcu/tree.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 531a328076bd..5f4336fadc28 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3649,6 +3649,11 @@ static void sync_sched_exp_handler(void *data)
 	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
 	    __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
 		return;
+	if (rcu_is_cpu_rrupt_from_idle()) {
+		rcu_report_exp_rdp(&rcu_sched_state,
+				   this_cpu_ptr(&rcu_sched_data), true);
+		return;
+	}
 	__this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
 	resched_cpu(smp_processor_id());
 }
-- 
2.5.2