From a2165e416878b325747f871df4b236b49bf61486 Mon Sep 17 00:00:00 2001 From: Paul E. McKenney Date: Sat, 12 May 2018 07:42:20 -0700 Subject: rcu: Don't funnel-lock above leaf node if GP in progress The old grace-period start code would acquire only the leaf's rcu_node structure's ->lock if that structure believed that a grace period was in progress. The new code advances to the leaf's parent in this case, needlessly acquiring then leaf's parent's ->lock. This commit therefore checks the grace-period state after marking the leaf with the need for the specified grace period, and if the leaf believes that a grace period is in progress, takes an early exit. Reported-by: Joel Fernandes Signed-off-by: Paul E. McKenney [ paulmck: Add "Startedleaf" tracing as suggested by Joel Fernandes. ] --- include/trace/events/rcu.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'include/trace/events/rcu.h') diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h index 7d3650cc9d30..5ab1df0a2801 100644 --- a/include/trace/events/rcu.h +++ b/include/trace/events/rcu.h @@ -91,8 +91,8 @@ TRACE_EVENT(rcu_grace_period, * * "Startleaf": Request a grace period based on leaf-node data. * "Prestarted": Someone beat us to the request - * "Startedleaf": Leaf-node start proved sufficient. - * "Startedleafroot": Leaf-node start proved sufficient after checking root. + * "Startedleaf": Leaf node marked for future GP. + * "Startedleafroot": All nodes from leaf to root marked for future GP. * "Startedroot": Requested a nocb grace period based on root-node data. * "NoGPkthread": The RCU grace-period kthread has not yet started. * "StartWait": Start waiting for the requested grace period. -- cgit v1.2.3-55-g7522