[PATCH v2 6/9] trace2: add timer events to perf and event target formats

["Jeff Hostetler via GitGitGadget" <gitgitgadget@gmail.com>]

From: Jeff Hostetler <jeffhost@microsoft.com>

Teach Trace2 "perf" and "event" formats to handle "timer" events for
stopwatch timers.  Update API documentation accordingly.

In a future commit, stopwatch timers will be added to the Trace2 API
and it will emit these "timer" events.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
---
 Documentation/technical/api-trace2.txt | 23 ++++++++++++++++++++
 trace2/tr2_tgt.h                       | 25 ++++++++++++++++++++++
 trace2/tr2_tgt_event.c                 | 29 ++++++++++++++++++++++++++
 trace2/tr2_tgt_normal.c                |  1 +
 trace2/tr2_tgt_perf.c                  | 27 ++++++++++++++++++++++++
 5 files changed, 105 insertions(+)

diff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt
index bb13ca3db8b..351d140879e 100644
--- a/Documentation/technical/api-trace2.txt
+++ b/Documentation/technical/api-trace2.txt
@@ -815,6 +815,29 @@ The "value" field may be an integer or a string.
 }
 ------------
 
+`"timer"`::
+	This event is generated at the end of the program and contains
+	statistics for a global stopwatch timer.
++
+------------
+{
+	"event":"timer",
+	...
+	"name":"test",      # timer name
+	"count":42,         # number of start+stop intervals
+	"ns_total":1234,    # sum of all intervals in nanoseconds
+	"ns_min":11,        # shortest interval in nanoseconds
+	"ns_max":789,       # longest interval in nanoseconds
+}
+------------
++
+Stopwatch timer data is independently collected by each thread and then
+aggregated for the whole program, so the total time reported here
+may exceed the "atexit" elapsed time of the program.
++
+Timer events may represent an individual thread or a summation across
+the entire program.  Summation events will have a unique thread name.
+
 == Example Trace2 API Usage
 
 Here is a hypothetical usage of the Trace2 API showing the intended
diff --git a/trace2/tr2_tgt.h b/trace2/tr2_tgt.h
index 65f94e15748..a41f91d09b5 100644
--- a/trace2/tr2_tgt.h
+++ b/trace2/tr2_tgt.h
@@ -96,6 +96,30 @@ typedef void(tr2_tgt_evt_printf_va_fl_t)(const char *file, int line,
 					 uint64_t us_elapsed_absolute,
 					 const char *fmt, va_list ap);
 
+/*
+ * Stopwatch timer event.  This function writes the previously accumulated
+ * stopwatch timer values to the event streams.  Unlike other Trace2 API
+ * events, this is decoupled from the data collection.
+ *
+ * This does not take a (file,line) pair because a timer event reports
+ * the cumulative time spend in the timer over a series of intervals
+ * -- it does not represent a single usage (like region or data events
+ * do).
+ *
+ * The thread name is optional.  If non-null it will override the
+ * value inherited from the caller's thread local storage.  This
+ * allows timer data to be aggregated and reported without associating
+ * it to a specific thread.
+ */
+typedef void(tr2_tgt_evt_timer_t)(uint64_t us_elapsed_absolute,
+				  const char *thread_name,
+				  const char *category,
+				  const char *timer_name,
+				  uint64_t interval_count,
+				  uint64_t ns_total_time,
+				  uint64_t ns_min_time,
+				  uint64_t ns_max_time);
+
 /*
  * "vtable" for a TRACE2 target.  Use NULL if a target does not want
  * to emit that message.
@@ -132,6 +156,7 @@ struct tr2_tgt {
 	tr2_tgt_evt_data_fl_t                   *pfn_data_fl;
 	tr2_tgt_evt_data_json_fl_t              *pfn_data_json_fl;
 	tr2_tgt_evt_printf_va_fl_t              *pfn_printf_va_fl;
+	tr2_tgt_evt_timer_t                     *pfn_timer;
 };
 /* clang-format on */
 
diff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c
index 4ce50944298..fe89e80bb1a 100644
--- a/trace2/tr2_tgt_event.c
+++ b/trace2/tr2_tgt_event.c
@@ -615,6 +615,34 @@ static void fn_data_json_fl(const char *file, int line,
 	}
 }
 
+static void fn_timer(uint64_t us_elapsed_absolute,
+		     const char *thread_name,
+		     const char *category,
+		     const char *timer_name,
+		     uint64_t interval_count,
+		     uint64_t ns_total_time,
+		     uint64_t ns_min_time,
+		     uint64_t ns_max_time)
+{
+	const char *event_name = "timer";
+	struct json_writer jw = JSON_WRITER_INIT;
+	double t_abs = (double)us_elapsed_absolute / 1000000.0;
+
+	jw_object_begin(&jw, 0);
+	event_fmt_prepare(event_name, __FILE__, __LINE__, NULL, &jw, thread_name);
+	jw_object_double(&jw, "t_abs", 6, t_abs);
+	jw_object_string(&jw, "name", timer_name);
+	jw_object_intmax(&jw, "count", interval_count);
+	jw_object_intmax(&jw, "ns_total", ns_total_time);
+	jw_object_intmax(&jw, "ns_min", ns_min_time);
+	jw_object_intmax(&jw, "ns_max", ns_max_time);
+
+	jw_end(&jw);
+
+	tr2_dst_write_line(&tr2dst_event, &jw.json);
+	jw_release(&jw);
+}
+
 struct tr2_tgt tr2_tgt_event = {
 	&tr2dst_event,
 
@@ -646,4 +674,5 @@ struct tr2_tgt tr2_tgt_event = {
 	fn_data_fl,
 	fn_data_json_fl,
 	NULL, /* printf */
+	fn_timer,
 };
diff --git a/trace2/tr2_tgt_normal.c b/trace2/tr2_tgt_normal.c
index 58d9e430f05..23a7e78dcaa 100644
--- a/trace2/tr2_tgt_normal.c
+++ b/trace2/tr2_tgt_normal.c
@@ -355,4 +355,5 @@ struct tr2_tgt tr2_tgt_normal = {
 	NULL, /* data */
 	NULL, /* data_json */
 	fn_printf_va_fl,
+	NULL, /* timer */
 };
diff --git a/trace2/tr2_tgt_perf.c b/trace2/tr2_tgt_perf.c
index c008fd08ae8..c07ffad1a32 100644
--- a/trace2/tr2_tgt_perf.c
+++ b/trace2/tr2_tgt_perf.c
@@ -555,6 +555,32 @@ static void fn_printf_va_fl(const char *file, int line,
 	strbuf_release(&buf_payload);
 }
 
+static void fn_timer(uint64_t us_elapsed_absolute,
+		     const char *thread_name,
+		     const char *category,
+		     const char *timer_name,
+		     uint64_t interval_count,
+		     uint64_t ns_total_time,
+		     uint64_t ns_min_time,
+		     uint64_t ns_max_time)
+{
+	const char *event_name = "timer";
+	struct strbuf buf_payload = STRBUF_INIT;
+
+	strbuf_addf(&buf_payload, ("name:%s"
+				   " count:%"PRIu64
+				   " ns_total:%"PRIu64
+				   " ns_min:%"PRIu64
+				   " ns_max:%"PRIu64),
+		    timer_name, interval_count, ns_total_time, ns_min_time,
+		    ns_max_time);
+
+	perf_io_write_fl(__FILE__, __LINE__, event_name, NULL,
+			 &us_elapsed_absolute, NULL,
+			 category, &buf_payload, thread_name);
+	strbuf_release(&buf_payload);
+}
+
 struct tr2_tgt tr2_tgt_perf = {
 	&tr2dst_perf,
 
@@ -586,4 +612,5 @@ struct tr2_tgt tr2_tgt_perf = {
 	fn_data_fl,
 	fn_data_json_fl,
 	fn_printf_va_fl,
+	fn_timer,
 };
-- 
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