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Subject[RFC] tracing: Add support for critical section event tracing
Date
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@goodmis.org>
Signed-off-by: Joel Fernandes <joelaf@google.com>
--
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
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