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Subject[PATCH tip/core/rcu 15/55] rcu: Event-trace markers for computing RCU CPU utilization
Date
From: Paul E. McKenney <paul.mckenney@linaro.org>

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>
---
include/trace/events/rcu.h | 73 ++++++++++++++++++++++++++++++++------------
kernel/rcutree.c | 16 +++++++++-
2 files changed, 68 insertions(+), 21 deletions(-)
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index db3f6e9..ab458eb 100644
--- 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
--- 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;
}

--
1.7.3.2


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