rcu: Add more tracing of expedited grace periods

This commit adds more tracing of expedited grace periods to enable
improved debugging of slowdowns.

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

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 0b50fda..e56a618 100644 (file)
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -179,6 +179,9 @@ TRACE_EVENT(rcu_grace_period_init,
  *
  *     "snap": Captured snapshot of expedited grace period sequence number.
  *     "start": Started a real expedited grace period.
+ *     "reset": Started resetting the tree
+ *     "select": Started selecting the CPUs to wait on.
+ *     "startwait": Started waiting on selected CPUs.
  *     "end": Ended a real expedited grace period.
  *     "endwake": Woke piggybackers up.
  *     "done": Someone else did the expedited grace period for us.

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 5d13f65..507a080 100644 (file)
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -77,12 +77,18 @@ static inline void rcu_seq_start(unsigned long *sp)
        WARN_ON_ONCE(rcu_seq_state(*sp) != 1);
 }
 
+/* Compute the end-of-grace-period value for the specified sequence number. */
+static inline unsigned long rcu_seq_endval(unsigned long *sp)
+{
+       return (*sp | RCU_SEQ_STATE_MASK) + 1;
+}
+
 /* Adjust sequence number for end of update-side operation. */
 static inline void rcu_seq_end(unsigned long *sp)
 {
        smp_mb(); /* Ensure update-side operation before counter increment. */
        WARN_ON_ONCE(!rcu_seq_state(*sp));
-       WRITE_ONCE(*sp, (*sp | RCU_SEQ_STATE_MASK) + 1);
+       WRITE_ONCE(*sp, rcu_seq_endval(sp));
 }
 
 /* Take a snapshot of the update side's sequence number. */

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 46d61b5..70ad12a 100644 (file)
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -29,6 +29,15 @@ static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
 }
 
 /*
+ * Return then value that expedited-grace-period counter will have
+ * at the end of the current grace period.
+ */
+static unsigned long rcu_exp_gp_seq_endval(struct rcu_state *rsp)
+{
+       return rcu_seq_endval(&rsp->expedited_sequence);
+}
+
+/*
  * Record the end of an expedited grace period.
  */
 static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
@@ -366,7 +375,9 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
        int ret;
        struct rcu_node *rnp;
 
+       trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("reset"));
        sync_exp_reset_tree(rsp);
+       trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("select"));
        rcu_for_each_leaf_node(rsp, rnp) {
                raw_spin_lock_irqsave_rcu_node(rnp, flags);
 
@@ -443,6 +454,7 @@ static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
        struct rcu_node *rnp_root = rcu_get_root(rsp);
        int ret;
 
+       trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("startwait"));
        jiffies_stall = rcu_jiffies_till_stall_check();
        jiffies_start = jiffies;