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>

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index db3f6e9..ab458eb 100644 (file)
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -7,29 +7,58 @@
 #include <linux/tracepoint.h>
 
 /*
- * Tracepoint for calling rcu_do_batch, performed to start callback invocation:
+ * Tracepoint for start/end markers used for utilization calculations.
+ * By convention, the string is of the following forms:
+ *
+ * "Start <activity>" -- Mark the start of the specified activity,
+ *                      such as "context switch".  Nesting is permitted.
+ * "End <activity>" -- Mark the end of the specified activity.
+ */
+TRACE_EVENT(rcu_utilization,
+
+       TP_PROTO(char *s),
+
+       TP_ARGS(s),
+
+       TP_STRUCT__entry(
+               __field(char *, s)
+       ),
+
+       TP_fast_assign(
+               __entry->s = s;
+       ),
+
+       TP_printk("%s", __entry->s)
+);
+
+/*
+ * Tracepoint for marking the beginning rcu_do_batch, performed to start
+ * RCU callback invocation.  The first argument is the total number of
+ * callbacks (including those that are not yet ready to be invoked),
+ * and the second argument is the current RCU-callback batch limit.
  */
 TRACE_EVENT(rcu_batch_start,
 
-       TP_PROTO(long callbacks_ready, int blimit),
+       TP_PROTO(long qlen, int blimit),
 
-       TP_ARGS(callbacks_ready, blimit),
+       TP_ARGS(qlen, blimit),
 
        TP_STRUCT__entry(
-               __field(        long,   callbacks_ready         )
-               __field(        int,    blimit                  )
+               __field(long, qlen)
+               __field(int, blimit)
        ),
 
        TP_fast_assign(
-               __entry->callbacks_ready        = callbacks_ready;
-               __entry->blimit                 = blimit;
+               __entry->qlen = qlen;
+               __entry->blimit = blimit;
        ),
 
-       TP_printk("CBs=%ld bl=%d", __entry->callbacks_ready, __entry->blimit)
+       TP_printk("CBs=%ld bl=%d", __entry->qlen, __entry->blimit)
 );
 
 /*
- * Tracepoint for the invocation of a single RCU callback
+ * Tracepoint for the invocation of a single RCU callback function.
+ * The argument is a pointer to the RCU callback itself.
  */
 TRACE_EVENT(rcu_invoke_callback,
 
@@ -38,20 +67,23 @@ TRACE_EVENT(rcu_invoke_callback,
        TP_ARGS(rhp),
 
        TP_STRUCT__entry(
-               __field(        void *, rhp     )
-               __field(        void *, func    )
+               __field(void *, rhp)
+               __field(void *, func)
        ),
 
        TP_fast_assign(
-               __entry->rhp    = rhp;
-               __entry->func   = rhp->func;
+               __entry->rhp = rhp;
+               __entry->func = rhp->func;
        ),
 
        TP_printk("rhp=%p func=%pf", __entry->rhp, __entry->func)
 );
 
 /*
- * Tracepoint for the invocation of a single RCU kfree callback
+ * Tracepoint for the invocation of a single RCU callback of the special
+ * kfree() form.  The first argument is a pointer to the RCU callback
+ * and the second argument is the offset of the callback within the
+ * enclosing RCU-protected data structure.
  */
 TRACE_EVENT(rcu_invoke_kfree_callback,
 
@@ -60,12 +92,12 @@ TRACE_EVENT(rcu_invoke_kfree_callback,
        TP_ARGS(rhp, offset),
 
        TP_STRUCT__entry(
-               __field(void *, rhp     )
-               __field(unsigned long,  offset  )
+               __field(void *, rhp)
+               __field(unsigned long, offset)
        ),
 
        TP_fast_assign(
-               __entry->rhp    = rhp;
+               __entry->rhp = rhp;
                __entry->offset = offset;
        ),
 
@@ -73,7 +105,8 @@ TRACE_EVENT(rcu_invoke_kfree_callback,
 );
 
 /*
- * Tracepoint for leaving rcu_do_batch, performed after callback invocation:
+ * Tracepoint for exiting rcu_do_batch after RCU callbacks have been
+ * invoked.  The first argument is the number of callbacks actually invoked.
  */
 TRACE_EVENT(rcu_batch_end,
 
@@ -82,11 +115,11 @@ TRACE_EVENT(rcu_batch_end,
        TP_ARGS(callbacks_invoked),
 
        TP_STRUCT__entry(
-               __field(        int,    callbacks_invoked               )
+               __field(int, callbacks_invoked)
        ),
 
        TP_fast_assign(
-               __entry->callbacks_invoked      = callbacks_invoked;
+               __entry->callbacks_invoked = callbacks_invoked;
        ),
 
        TP_printk("CBs-invoked=%d", __entry->callbacks_invoked)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 45dcc20..2a9643b 100644 (file)
--- 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;
 }