diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2018-05-12 17:42:20 +0300 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2018-07-13 01:38:52 +0300 |
| commit | a2165e416878b325747f871df4b236b49bf61486 (patch) | |
| tree | f34e198b527f5a69380b72a311076e1f26e26268 | |
| parent | e1333462e3cf933ab860c693ef1ff50775c7ea7f (diff) | |
| download | linux-a2165e416878b325747f871df4b236b49bf61486.tar.xz | |
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 <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Add "Startedleaf" tracing as suggested by Joel Fernandes. ]
| -rw-r--r-- | include/trace/events/rcu.h | 4 | ||||
| -rw-r--r-- | kernel/rcu/tree.c | 9 |
2 files changed, 11 insertions, 2 deletions
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. diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 5643c135fb06..24a79e85b81f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1590,6 +1590,15 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, goto unlock_out; } rnp_root->gp_seq_needed = c; + if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) { + /* + * We just marked the leaf, and a grace period + * is in progress, which means that rcu_gp_cleanup() + * will see the marking. Bail to reduce contention. + */ + trace_rcu_this_gp(rnp, rdp, c, TPS("Startedleaf")); + goto unlock_out; + } if (rnp_root != rnp && rnp_root->parent != NULL) raw_spin_unlock_rcu_node(rnp_root); if (!rnp_root->parent) |