rcu: Make expedited RCU-sched grace period immediately detect idle

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@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 531a328..5f4336f 100644 (file)
--- 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());
 }