rcu: Track rcu_nocb_kthread()'s sleeping and awakening

This commit adds event traces to track all of rcu_nocb_kthread()'s
blocking and awakening.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

2 files changed, 18 insertions, 1 deletions

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 4301cd9e3ee5..a087d82ed431 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -183,8 +183,12 @@ TRACE_EVENT(rcu_grace_period_init,
  *      "WakeOvf": Wake rcuo kthread, CB list is huge.
  *      "WakeNot": Don't wake rcuo kthread.
  *      "WakeNotPoll": Don't wake rcuo kthread because it is polling.
+ *      "Poll": Start of new polling cycle for rcu_nocb_poll.
+ *      "Sleep": Sleep waiting for CBs for !rcu_nocb_poll.
  *      "WokeEmpty": rcuo kthread woke to find empty list.
  *      "WokeNonEmpty": rcuo kthread woke to find non-empty list.
+ *      "WaitQueue": Enqueue partially done, timed wait for it to complete.
+ *      "WokeQueue": Partial enqueue now complete.
  */
 TRACE_EVENT(rcu_nocb_wake,
 
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 24b01b69be92..21205b185340 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -2230,6 +2230,7 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
 static int rcu_nocb_kthread(void *arg)
 {
         int c, cl;
+        bool firsttime = 1;
         struct rcu_head *list;
         struct rcu_head *next;
         struct rcu_head **tail;
@@ -2238,8 +2239,15 @@ static int rcu_nocb_kthread(void *arg)
         /* Each pass through this loop invokes one batch of callbacks */
         for (;;) {
                 /* If not polling, wait for next batch of callbacks. */
-                if (!rcu_nocb_poll)
+                if (!rcu_nocb_poll) {
+                        trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                            TPS("Sleep"));
                         wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
+                } else if (firsttime) {
+                        firsttime = 0;
+                        trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                            TPS("Poll"));
+                }
                 list = ACCESS_ONCE(rdp->nocb_head);
                 if (!list) {
                         if (!rcu_nocb_poll)
@@ -2249,6 +2257,7 @@ static int rcu_nocb_kthread(void *arg)
                         flush_signals(current);
                         continue;
                 }
+                firsttime = 1;
                 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
                                     TPS("WokeNonEmpty"));
 
@@ -2271,7 +2280,11 @@ static int rcu_nocb_kthread(void *arg)
                         next = list->next;
                         /* Wait for enqueuing to complete, if needed. */
                         while (next == NULL && &list->next != tail) {
+                                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                                    TPS("WaitQueue"));
                                 schedule_timeout_interruptible(1);
+                                trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
+                                                    TPS("WokeQueue"));
                                 next = list->next;
                         }
                         debug_rcu_head_unqueue(list);