[RFC] tracing: Add support for critical section event tracing

[Joel Fernandes]

Critical section trace events can be used for tracing the start and
end of a critical section which can be used by a trace viewer like
systrace to graphically view the start and end of a critical section and
correlate them with latencies and scheduling issues.

Reason for starting critical section:
Either preemption or interrupts were turned off.
Reason for ending critical section:
Both preemption and interrupts are now turned back on.

Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Joel Fernandes <joelaf@xxxxxxxxxx>
--
Here's an example of how Android's systrace will be using it to show critical
sections as a gantt chart: http://imgur.com/download/TZplEVp
---
 include/trace/events/critical.h | 55 +++++++++++++++++++++++++++++++
 kernel/trace/Kconfig            |  6 ++++
 kernel/trace/trace_irqsoff.c    | 73 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 134 insertions(+)
 create mode 100644 include/trace/events/critical.h

diff --git a/include/trace/events/critical.h b/include/trace/events/critical.h
new file mode 100644
index 000000000000..bfd58dd4f48f
--- /dev/null
+++ b/include/trace/events/critical.h
@@ -0,0 +1,55 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM critical
+
+#if !defined(_TRACE_CRITICAL_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_CRITICAL_H
+
+#include <linux/ktime.h>
+#include <linux/tracepoint.h>
+#include <linux/string.h>
+
+TRACE_EVENT(critical_start,
+
+	TP_PROTO(unsigned long ip, unsigned long parent_ip),
+
+	TP_ARGS(ip, parent_ip),
+
+	TP_STRUCT__entry(
+		__array(char, func, 16)
+		__array(char, parent, 16)
+	),
+
+	TP_fast_assign(
+		snprintf(__entry->func, 16, "%pf", (void *)ip);
+		snprintf(__entry->parent, 16, "%pf", (void *)parent_ip);
+	),
+
+	TP_printk("caller=%s parent=%s\n",
+		  __entry->func,
+		  __entry->parent)
+);
+
+TRACE_EVENT(critical_end,
+
+	TP_PROTO(unsigned long ip, unsigned long parent_ip),
+
+	TP_ARGS(ip, parent_ip),
+
+	TP_STRUCT__entry(
+		__array(char, func, 16)
+		__array(char, parent, 16)
+	),
+
+	TP_fast_assign(
+		snprintf(__entry->func, 16, "%pf", (void *)ip);
+		snprintf(__entry->parent, 16, "%pf", (void *)parent_ip);
+	),
+
+	TP_printk("caller=%s parent=%s\n",
+		  __entry->func,
+		  __entry->parent)
+);
+#endif /* _TRACE_CRITICAL_H */
+
+/* This part ust be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index d5038005eb5d..986a07985360 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -208,6 +208,12 @@ config PREEMPT_TRACER
 	  enabled. This option and the irqs-off timing option can be
 	  used together or separately.)
 
+config TRACE_CRITICAL_SECTION_EVENTS
+	bool "Trace critical sections as trace events"
+	default n
+	select IRQSOFF_TRACER
+	select PREEMPT_TRACER
+
 config SCHED_TRACER
 	bool "Scheduling Latency Tracer"
 	select GENERIC_TRACER
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 7758bc0617cb..a14ce6185885 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -13,6 +13,8 @@
 #include <linux/uaccess.h>
 #include <linux/module.h>
 #include <linux/ftrace.h>
+#define CREATE_TRACE_POINTS
+#include <trace/events/critical.h>
 
 #include "trace.h"
 
@@ -20,6 +22,7 @@ static struct trace_array		*irqsoff_trace __read_mostly;
 static int				tracer_enabled __read_mostly;
 
 static DEFINE_PER_CPU(int, tracing_cpu);
+static DEFINE_PER_CPU(int, tracing_events_cpu);
 
 static DEFINE_RAW_SPINLOCK(max_trace_lock);
 
@@ -362,6 +365,44 @@ check_critical_timing(struct trace_array *tr,
 	__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
 }
 
+#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
+/*
+ * Called when either preempt or irq are turned off
+ */
+static inline void
+start_critical_event(unsigned long ip, unsigned long parent_ip)
+{
+	int cpu;
+
+	cpu = raw_smp_processor_id();
+
+	if (per_cpu(tracing_events_cpu, cpu))
+		return;
+
+	trace_critical_start(ip, parent_ip);
+
+	per_cpu(tracing_events_cpu, cpu) = 1;
+}
+
+/*
+ * Called when both preempt and irq are turned back on
+ */
+static inline void
+stop_critical_event(unsigned long ip, unsigned long parent_ip)
+{
+	int cpu;
+
+	cpu = raw_smp_processor_id();
+
+	if (unlikely(per_cpu(tracing_events_cpu, cpu)))
+		per_cpu(tracing_events_cpu, cpu) = 0;
+	else
+		return;
+
+	trace_critical_end(ip, parent_ip);
+}
+#endif
+
 static inline void
 start_critical_timing(unsigned long ip, unsigned long parent_ip)
 {
@@ -434,6 +475,10 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip)
 /* start and stop critical timings used to for stoppage (in idle) */
 void start_critical_timings(void)
 {
+#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
+	if (irqs_disabled() || preempt_count())
+		start_critical_event(CALLER_ADDR0, CALLER_ADDR1);
+#endif
 	if (preempt_trace() || irq_trace())
 		start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
 }
@@ -441,6 +486,10 @@ EXPORT_SYMBOL_GPL(start_critical_timings);
 
 void stop_critical_timings(void)
 {
+#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
+	if (irqs_disabled() || preempt_count())
+		stop_critical_event(CALLER_ADDR0, CALLER_ADDR1);
+#endif
 	if (preempt_trace() || irq_trace())
 		stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
 }
@@ -483,6 +532,10 @@ inline void print_irqtrace_events(struct task_struct *curr)
  */
 void trace_hardirqs_on(void)
 {
+#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
+	if (!preempt_count())
+		stop_critical_event(CALLER_ADDR0, CALLER_ADDR1);
+#endif
 	if (!preempt_trace() && irq_trace())
 		stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
 }
@@ -490,6 +543,10 @@ EXPORT_SYMBOL(trace_hardirqs_on);
 
 void trace_hardirqs_off(void)
 {
+#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
+	if (!preempt_count())
+		start_critical_event(CALLER_ADDR0, CALLER_ADDR1);
+#endif
 	if (!preempt_trace() && irq_trace())
 		start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
 }
@@ -497,6 +554,10 @@ EXPORT_SYMBOL(trace_hardirqs_off);
 
 __visible void trace_hardirqs_on_caller(unsigned long caller_addr)
 {
+#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
+	if (!preempt_count())
+		stop_critical_event(CALLER_ADDR0, caller_addr);
+#endif
 	if (!preempt_trace() && irq_trace())
 		stop_critical_timing(CALLER_ADDR0, caller_addr);
 }
@@ -504,6 +565,10 @@ EXPORT_SYMBOL(trace_hardirqs_on_caller);
 
 __visible void trace_hardirqs_off_caller(unsigned long caller_addr)
 {
+#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
+	if (!preempt_count())
+		start_critical_event(CALLER_ADDR0, caller_addr);
+#endif
 	if (!preempt_trace() && irq_trace())
 		start_critical_timing(CALLER_ADDR0, caller_addr);
 }
@@ -515,12 +580,20 @@ EXPORT_SYMBOL(trace_hardirqs_off_caller);
 #ifdef CONFIG_PREEMPT_TRACER
 void trace_preempt_on(unsigned long a0, unsigned long a1)
 {
+#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
+	if (!irqs_disabled())
+		stop_critical_event(a0, a1);
+#endif
 	if (preempt_trace() && !irq_trace())
 		stop_critical_timing(a0, a1);
 }
 
 void trace_preempt_off(unsigned long a0, unsigned long a1)
 {
+#ifdef CONFIG_TRACE_CRITICAL_SECTION_EVENTS
+	if (!irqs_disabled())
+		start_critical_event(a0, a1);
+#endif
 	if (preempt_trace() && !irq_trace())
 		start_critical_timing(a0, a1);
 }
-- 
2.12.2.715.g7642488e1d-goog