rcu: Add boosting to TREE_PREEMPT_RCU tracing

Includes total number of tasks boosted, number boosted on behalf of each
of normal and expedited grace periods, and statistics on attempts to
initiate boosting that failed for various reasons.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

1 files changed, 38 insertions, 4 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 4e486255df63..07d346445d12 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1073,6 +1073,33 @@ static void __init __rcu_init_preempt(void)
 
 #include "rtmutex_common.h"
 
+#ifdef CONFIG_RCU_TRACE
+
+static void rcu_initiate_boost_trace(struct rcu_node *rnp)
+{
+        if (list_empty(&rnp->blkd_tasks))
+                rnp->n_balk_blkd_tasks++;
+        else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
+                rnp->n_balk_exp_gp_tasks++;
+        else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
+                rnp->n_balk_boost_tasks++;
+        else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
+                rnp->n_balk_notblocked++;
+        else if (rnp->gp_tasks != NULL &&
+                 ULONG_CMP_GE(jiffies, rnp->boost_time))
+                rnp->n_balk_notyet++;
+        else
+                rnp->n_balk_nos++;
+}
+
+#else /* #ifdef CONFIG_RCU_TRACE */
+
+static void rcu_initiate_boost_trace(struct rcu_node *rnp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_TRACE */
+
 /*
  * Carry out RCU priority boosting on the task indicated by ->exp_tasks
  * or ->boost_tasks, advancing the pointer to the next task in the
@@ -1108,10 +1135,14 @@ static int rcu_boost(struct rcu_node *rnp)
          * expedited grace period must boost all blocked tasks, including
          * those blocking the pre-existing normal grace period.
          */
-        if (rnp->exp_tasks != NULL)
+        if (rnp->exp_tasks != NULL) {
                 tb = rnp->exp_tasks;
-        else
+                rnp->n_exp_boosts++;
+        } else {
                 tb = rnp->boost_tasks;
+                rnp->n_normal_boosts++;
+        }
+        rnp->n_tasks_boosted++;
 
         /*
          * We boost task t by manufacturing an rt_mutex that appears to
@@ -1197,8 +1228,10 @@ static void rcu_initiate_boost(struct rcu_node *rnp)
 {
         struct task_struct *t;
 
-        if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL)
+        if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
+                rnp->n_balk_exp_gp_tasks++;
                 return;
+        }
         if (rnp->exp_tasks != NULL ||
             (rnp->gp_tasks != NULL &&
              rnp->boost_tasks == NULL &&
@@ -1209,7 +1242,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp)
                 t = rnp->boost_kthread_task;
                 if (t != NULL)
                         wake_up_process(t);
-        }
+        } else
+                rcu_initiate_boost_trace(rnp);
 }
 
 /*