From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit c337f8f58ed7cf150651d232af8222421a71463d upstream.
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@xxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Tested-by: Tibor Billes <tbilles@xxxxxxx>
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
kernel/rcutree_plugin.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index fd71cef0d789..d9cd0c2e34cb 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1739,6 +1739,8 @@ 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;
}
--
1.9.0
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