rcu: Event-trace markers for computing RCU CPU utilization

This commit adds the trace_rcu_utilization() marker that is to be
used to allow postprocessing scripts compute RCU's CPU utilization,
give or take event-trace overhead.  Note that we do not include RCU's
dyntick-idle interface because event tracing requires RCU protection,
which is not available in dyntick-idle mode.

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

1 files changed, 15 insertions, 1 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 45dcc2036a1e..2a9643bd6ae9 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -184,8 +184,10 @@ void rcu_bh_qs(int cpu)
  */
 void rcu_note_context_switch(int cpu)
 {
+	trace_rcu_utilization("Start context switch");
 	rcu_sched_qs(cpu);
 	rcu_preempt_note_context_switch(cpu);
+	trace_rcu_utilization("End context switch");
 }
 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
 
@@ -1275,6 +1277,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
  */
 void rcu_check_callbacks(int cpu, int user)
 {
+	trace_rcu_utilization("Start scheduler-tick");
 	if (user ||
 	    (idle_cpu(cpu) && rcu_scheduler_active &&
 	     !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
@@ -1308,6 +1311,7 @@ void rcu_check_callbacks(int cpu, int user)
 	rcu_preempt_check_callbacks(cpu);
 	if (rcu_pending(cpu))
 		invoke_rcu_core();
+	trace_rcu_utilization("End scheduler-tick");
 }
 
 #ifdef CONFIG_SMP
@@ -1369,10 +1373,14 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 	unsigned long flags;
 	struct rcu_node *rnp = rcu_get_root(rsp);
 
-	if (!rcu_gp_in_progress(rsp))
+	trace_rcu_utilization("Start fqs");
+	if (!rcu_gp_in_progress(rsp)) {
+		trace_rcu_utilization("End fqs");
 		return;  /* No grace period in progress, nothing to force. */
+	}
 	if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) {
 		rsp->n_force_qs_lh++; /* Inexact, can lose counts.  Tough! */
+		trace_rcu_utilization("End fqs");
 		return;	/* Someone else is already on the job. */
 	}
 	if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies))
@@ -1421,11 +1429,13 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
 		raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */
 		rsp->fqs_need_gp = 0;
 		rcu_start_gp(rsp, flags); /* releases rnp->lock */
+		trace_rcu_utilization("End fqs");
 		return;
 	}
 	raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
 unlock_fqs_ret:
 	raw_spin_unlock_irqrestore(&rsp->fqslock, flags);
+	trace_rcu_utilization("End fqs");
 }
 
 #else /* #ifdef CONFIG_SMP */
@@ -1481,6 +1491,7 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
  */
 static void rcu_process_callbacks(struct softirq_action *unused)
 {
+	trace_rcu_utilization("Start RCU core");
 	__rcu_process_callbacks(&rcu_sched_state,
 				&__get_cpu_var(rcu_sched_data));
 	__rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
@@ -1488,6 +1499,7 @@ static void rcu_process_callbacks(struct softirq_action *unused)
 
 	/* If we are last CPU on way to dyntick-idle mode, accelerate it. */
 	rcu_needs_cpu_flush();
+	trace_rcu_utilization("End RCU core");
 }
 
 /*
@@ -1910,6 +1922,7 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
 	struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
 	struct rcu_node *rnp = rdp->mynode;
 
+	trace_rcu_utilization("Start CPU hotplug");
 	switch (action) {
 	case CPU_UP_PREPARE:
 	case CPU_UP_PREPARE_FROZEN:
@@ -1945,6 +1958,7 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
 	default:
 		break;
 	}
+	trace_rcu_utilization("End CPU hotplug");
 	return NOTIFY_OK;
 }