[PATCH v2 2/3] tracing: Add trace_irqsoff tracepoints

[Binoy Jayan]

This work is based on work by Daniel Wagner. A few tracepoints are added
at the end of the critical section. With the hist trigger in place, the
hist trigger plots may be generated, with per-cpu breakdown of events
captured. It is based on linux kernel's event infrastructure.

The following filter(s) may be used

'hist:key=latency.log2:val=hitcount:sort=latency'
'hist:key=cpu,latency:val=hitcount:sort=latency if cpu==1'
'hist:key=common_pid.execname'

This captures only the latencies introduced by disabled irqs and
preemption. Additional per process data has to be captured to calculate
the effective latencies introduced for individual processes.

Initial work - latency.patch

[1] https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit/?h=v3.14-rt-rebase&id=56d50cc34943bbba12b8c5942ee1ae3b29f73acb

Signed-off-by: Binoy Jayan <binoy.jayan@xxxxxxxxxx>
---
 include/trace/events/latency.h | 43 ++++++++++++++++++++++++++++++++++++++++++
 kernel/trace/trace_irqsoff.c   | 42 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 84 insertions(+), 1 deletion(-)
 create mode 100644 include/trace/events/latency.h

diff --git a/include/trace/events/latency.h b/include/trace/events/latency.h
new file mode 100644
index 0000000..77896c7
--- /dev/null
+++ b/include/trace/events/latency.h
@@ -0,0 +1,43 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM latency
+
+#if !defined(_TRACE_HIST_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_HIST_H
+
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(latency_template,
+	TP_PROTO(int cpu, cycles_t latency),
+
+	TP_ARGS(cpu, latency),
+
+	TP_STRUCT__entry(
+		__field(int,		cpu)
+		__field(cycles_t,	latency)
+	),
+
+	TP_fast_assign(
+		__entry->cpu		= cpu;
+		__entry->latency	= latency;
+	),
+
+	TP_printk("cpu=%d, latency=%lu", __entry->cpu,
+			(unsigned long) __entry->latency)
+);
+
+DEFINE_EVENT(latency_template, latency_irqs,
+	    TP_PROTO(int cpu, cycles_t latency),
+	    TP_ARGS(cpu, latency));
+
+DEFINE_EVENT(latency_template, latency_preempt,
+	    TP_PROTO(int cpu, cycles_t latency),
+	    TP_ARGS(cpu, latency));
+
+DEFINE_EVENT(latency_template, latency_critical_timings,
+	    TP_PROTO(int cpu, cycles_t latency),
+	    TP_ARGS(cpu, latency));
+
+#endif /* _TRACE_HIST_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 03cdff8..3fcf446 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -13,14 +13,22 @@
 #include <linux/uaccess.h>
 #include <linux/module.h>
 #include <linux/ftrace.h>
+#include <linux/percpu-defs.h>
+
+#include <trace/events/sched.h>
 
 #include "trace.h"
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/latency.h>
+
 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(cycle_t __maybe_unused, ts_irqs);
+static DEFINE_PER_CPU(cycle_t __maybe_unused, ts_preempt);
+static DEFINE_PER_CPU(cycle_t __maybe_unused, ts_critical_timings);
 static DEFINE_RAW_SPINLOCK(max_trace_lock);
 
 enum {
@@ -419,9 +427,17 @@ stop_critical_timing(unsigned long ip, unsigned long parent_ip)
 	atomic_dec(&data->disabled);
 }
 
+static inline cycle_t get_delta(cycle_t __percpu *ts)
+{
+	return (cycle_t) trace_clock_local() - this_cpu_read(*ts);
+}
 /* start and stop critical timings used to for stoppage (in idle) */
 void start_critical_timings(void)
 {
+	if (trace_latency_critical_timings_enabled())
+		this_cpu_write(ts_critical_timings,
+			(cycle_t) trace_clock_local());
+
 	if (preempt_trace() || irq_trace())
 		start_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
 }
@@ -431,6 +447,13 @@ void stop_critical_timings(void)
 {
 	if (preempt_trace() || irq_trace())
 		stop_critical_timing(CALLER_ADDR0, CALLER_ADDR1);
+
+	if (trace_latency_critical_timings_enabled()) {
+		trace_latency_critical_timings(
+			raw_smp_processor_id(),
+			get_delta(&ts_critical_timings));
+	}
+
 }
 EXPORT_SYMBOL_GPL(stop_critical_timings);
 
@@ -438,6 +461,10 @@ EXPORT_SYMBOL_GPL(stop_critical_timings);
 #ifdef CONFIG_PROVE_LOCKING
 void time_hardirqs_on(unsigned long a0, unsigned long a1)
 {
+	if (trace_latency_irqs_enabled()) {
+		trace_latency_irqs(raw_smp_processor_id(),
+			get_delta(&ts_irqs));
+	}
 	if (!preempt_trace() && irq_trace())
 		stop_critical_timing(a0, a1);
 }
@@ -446,6 +473,10 @@ void time_hardirqs_off(unsigned long a0, unsigned long a1)
 {
 	if (!preempt_trace() && irq_trace())
 		start_critical_timing(a0, a1);
+
+	if (trace_latency_irqs_enabled()) {
+                this_cpu_write(ts_irqs, (cycle_t) trace_clock_local());
+	}
 }
 
 #else /* !CONFIG_PROVE_LOCKING */
@@ -503,6 +534,11 @@ EXPORT_SYMBOL(trace_hardirqs_off_caller);
 #ifdef CONFIG_PREEMPT_TRACER
 void trace_preempt_on(unsigned long a0, unsigned long a1)
 {
+	if (trace_latency_preempt_enabled()) {
+		trace_latency_preempt(raw_smp_processor_id(),
+			get_delta(&ts_preempt));
+	}
+
 	if (preempt_trace() && !irq_trace())
 		stop_critical_timing(a0, a1);
 }
@@ -511,6 +547,10 @@ void trace_preempt_off(unsigned long a0, unsigned long a1)
 {
 	if (preempt_trace() && !irq_trace())
 		start_critical_timing(a0, a1);
+
+	if (trace_latency_preempt_enabled()) {
+                this_cpu_write(ts_preempt, (cycle_t) trace_clock_local());
+	}
 }
 #endif /* CONFIG_PREEMPT_TRACER */
 
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