rcu: Add long-term CPU kicking

This commit prepares for the removal of short-term CPU kicking (in a
subsequent commit).  It does so by starting to invoke resched_cpu()
for each holdout at each force-quiescent-state interval that is more
than halfway through the stall-warning interval.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 83bf054e194e60db416e3c82d7bba6fe08bed588..0e61b62e3f4a42a0836458a9299580145c906289 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
                         rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
            ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
                resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
+       /*
+        * If more than halfway to RCU CPU stall-warning time, do
+        * a resched_cpu() to try to loosen things up a bit.
+        */
+       if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
+               resched_cpu(rdp->cpu);
 
        return 0;
 }