rcu: Throttle invoke_rcu_core() invocations due to non-lazy callbacks

If a non-lazy callback arrives on a CPU that has previously gone idle
with no non-lazy callbacks, invoke_rcu_core() forces the RCU core to
run.  However, it does not update the conditions, which could result
in several closely spaced invocations of the RCU core, which in turn
could result in an excessively high context-switch rate and resulting
high overhead.

This commit therefore updates the ->all_lazy and ->nonlazy_posted_snap
fields to prevent closely spaced invocations.

Reported-by: Tibor Billes <tbilles@gmx.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Tibor Billes <tbilles@gmx.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index d81e3856fa91579016ce6e5568a5eabeee0f8dcd..2c15d7c10684b4fd6e2c9fff89afd8f5955a4cfd 100644 (file)
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1745,6 +1745,8 @@ static void rcu_prepare_for_idle(int cpu)
         */
        if (rdtp->all_lazy &&
            rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
+               rdtp->all_lazy = false;
+               rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
                invoke_rcu_core();
                return;
        }