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-rw-r--r--kernel/rcu/tree.c16
-rw-r--r--kernel/rcu/tree.h2
-rw-r--r--kernel/rcu/tree_trace.c4
3 files changed, 19 insertions, 3 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f66f6e7730bc..3af0dee2d045 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3356,6 +3356,22 @@ static struct rcu_node *exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
struct rcu_node *rnp1 = NULL;
/*
+ * First try directly acquiring the root lock in order to reduce
+ * latency in the common case where expedited grace periods are
+ * rare. We check mutex_is_locked() to avoid pathological levels of
+ * memory contention on ->exp_funnel_mutex in the heavy-load case.
+ */
+ rnp0 = rcu_get_root(rsp);
+ if (!mutex_is_locked(&rnp0->exp_funnel_mutex)) {
+ if (mutex_trylock(&rnp0->exp_funnel_mutex)) {
+ if (sync_exp_work_done(rsp, rnp0, NULL,
+ &rsp->expedited_workdone0, s))
+ return NULL;
+ return rnp0;
+ }
+ }
+
+ /*
* Each pass through the following loop works its way
* up the rcu_node tree, returning if others have done the
* work or otherwise falls through holding the root rnp's
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 543ba726396c..80d974df0ea0 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -493,7 +493,7 @@ struct rcu_state {
/* End of fields guarded by barrier_mutex. */
unsigned long expedited_sequence; /* Take a ticket. */
- atomic_long_t expedited_tryfail; /* # acquisition failures. */
+ atomic_long_t expedited_workdone0; /* # done by others #0. */
atomic_long_t expedited_workdone1; /* # done by others #1. */
atomic_long_t expedited_workdone2; /* # done by others #2. */
atomic_long_t expedited_workdone3; /* # done by others #3. */
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index ec62369f1b02..6fc4c5ff3bb5 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -185,9 +185,9 @@ static int show_rcuexp(struct seq_file *m, void *v)
{
struct rcu_state *rsp = (struct rcu_state *)m->private;
- seq_printf(m, "t=%lu tf=%lu wd1=%lu wd2=%lu wd3=%lu n=%lu enq=%d sc=%lu\n",
+ seq_printf(m, "s=%lu wd0=%lu wd1=%lu wd2=%lu wd3=%lu n=%lu enq=%d sc=%lu\n",
rsp->expedited_sequence,
- atomic_long_read(&rsp->expedited_tryfail),
+ atomic_long_read(&rsp->expedited_workdone0),
atomic_long_read(&rsp->expedited_workdone1),
atomic_long_read(&rsp->expedited_workdone2),
atomic_long_read(&rsp->expedited_workdone3),