[PATCH V8 8/8] perf tools: handle PERF_RECORD_LOST_SAMPLES

[Kan Liang]

From: Kan Liang <kan.liang@xxxxxxxxx>

This patch modified the perf tool to handle the new RECORD type,
PERF_RECORD_LOST_SAMPLES.
The number of lost-sample events is stored in
.nr_events[PERF_EVENT_LOST_SAMPLES]. While the exact number of samples
which the kernel dropped is stored in total_lost_samples.
When the percentage of dropped samples is greater than 5%, a warning
will be sent out.

Here are some examples:

Eg 1, Recording different frequently-occurring events is safe with the
      patch. Only a very low drop rate is associated with such actions.

$ perf record -e '{cycles:p,instructions:p}' -c 20003 --no-time ~/tchain
~/tchain
[perf record: Woken up 148 times to write data]
[perf record: Captured and wrote 36.922 MB perf.data (1206322 samples)]

$ perf report -D | tail
          SAMPLE events:    1206322
           MMAP2 events:          5
     LOST_SAMPLE events:       2559
  FINISHED_ROUND events:        148
cycles:p stats:
           TOTAL events:     606278
          SAMPLE events:     606278
instructions:p stats:
           TOTAL events:     600044
          SAMPLE events:     600044

Eg 2, Recording the same thing multiple times can lead to high drop
      rate, but it is not a useful configuration.

$ perf record -e '{cycles:p,cycles:p}' -c 20003 --no-time ~/tchain
[perf record: Woken up 1 times to write data]
Warning:
Processed 600592 samples and lost 99.73% samples!
[perf record: Captured and wrote 0.121 MB perf.data (1629 samples)]

Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
---
 tools/perf/util/event.c   |  9 +++++++++
 tools/perf/util/event.h   | 18 ++++++++++++++++++
 tools/perf/util/machine.c | 10 ++++++++++
 tools/perf/util/machine.h |  2 ++
 tools/perf/util/session.c | 19 +++++++++++++++++++
 tools/perf/util/tool.h    |  1 +
 6 files changed, 59 insertions(+)

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index db52609..2daadc8 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -25,6 +25,7 @@ static const char *perf_event__names[] = {
 	[PERF_RECORD_SAMPLE]			= "SAMPLE",
 	[PERF_RECORD_AUX]			= "AUX",
 	[PERF_RECORD_ITRACE_START]		= "ITRACE_START",
+	[PERF_RECORD_LOST_SAMPLES]		= "LOST_SAMPLES",
 	[PERF_RECORD_HEADER_ATTR]		= "ATTR",
 	[PERF_RECORD_HEADER_EVENT_TYPE]		= "EVENT_TYPE",
 	[PERF_RECORD_HEADER_TRACING_DATA]	= "TRACING_DATA",
@@ -713,6 +714,14 @@ int perf_event__process_itrace_start(struct perf_tool *tool __maybe_unused,
 	return machine__process_itrace_start_event(machine, event);
 }
 
+int perf_event__process_lost_samples(struct perf_tool *tool __maybe_unused,
+				     union perf_event *event,
+				     struct perf_sample *sample,
+				     struct machine *machine)
+{
+	return machine__process_lost_samples_event(machine, event, sample);
+}
+
 size_t perf_event__fprintf_mmap(union perf_event *event, FILE *fp)
 {
 	return fprintf(fp, " %d/%d: [%#" PRIx64 "(%#" PRIx64 ") @ %#" PRIx64 "]: %c %s\n",
diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
index 7eecd5e..abfc579 100644
--- a/tools/perf/util/event.h
+++ b/tools/perf/util/event.h
@@ -52,6 +52,12 @@ struct lost_event {
 	u64 lost;
 };
 
+struct lost_samples_event {
+	struct perf_event_header header;
+	u64 id;
+	u64 lost;
+};
+
 /*
  * PERF_FORMAT_ENABLED | PERF_FORMAT_RUNNING | PERF_FORMAT_ID
  */
@@ -235,6 +241,12 @@ enum auxtrace_error_type {
  * total_lost tells exactly how many events the kernel in fact lost, i.e. it is
  * the sum of all struct lost_event.lost fields reported.
  *
+ * The kernel discards mixed up samples and sends the number in a
+ * PERF_RECORD_LOST_SAMPLES event. The number of lost-samples events is stored
+ * in .nr_events[PERF_EVENT_LOST_SAMPLES] while total_lost_samples tells
+ * exactly how many samples the kernel in fact dropped, i.e. it is the sum of
+ * all struct lost_samples_event.lost fields reported.
+ *
  * The total_period is needed because by default auto-freq is used, so
  * multipling nr_events[PERF_EVENT_SAMPLE] by a frequency isn't possible to get
  * the total number of low level events, it is necessary to to sum all struct
@@ -244,6 +256,7 @@ struct events_stats {
 	u64 total_period;
 	u64 total_non_filtered_period;
 	u64 total_lost;
+	u64 total_lost_samples;
 	u64 total_invalid_chains;
 	u32 nr_events[PERF_RECORD_HEADER_MAX];
 	u32 nr_non_filtered_samples;
@@ -342,6 +355,7 @@ union perf_event {
 	struct comm_event		comm;
 	struct fork_event		fork;
 	struct lost_event		lost;
+	struct lost_samples_event	lost_samples;
 	struct read_event		read;
 	struct throttle_event		throttle;
 	struct sample_event		sample;
@@ -390,6 +404,10 @@ int perf_event__process_lost(struct perf_tool *tool,
 			     union perf_event *event,
 			     struct perf_sample *sample,
 			     struct machine *machine);
+int perf_event__process_lost_samples(struct perf_tool *tool,
+				     union perf_event *event,
+				     struct perf_sample *sample,
+				     struct machine *machine);
 int perf_event__process_aux(struct perf_tool *tool,
 			    union perf_event *event,
 			    struct perf_sample *sample,
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 2f47110..4623dd7 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -458,6 +458,14 @@ int machine__process_lost_event(struct machine *machine __maybe_unused,
 	return 0;
 }
 
+int machine__process_lost_samples_event(struct machine *machine __maybe_unused,
+					union perf_event *event, struct perf_sample *sample __maybe_unused)
+{
+	dump_printf(": id:%" PRIu64 ": lost samples :%" PRIu64 "\n",
+		    event->lost.id, event->lost.lost);
+	return 0;
+}
+
 static struct dso*
 machine__module_dso(struct machine *machine, struct kmod_path *m,
 		    const char *filename)
@@ -1351,6 +1359,8 @@ int machine__process_event(struct machine *machine, union perf_event *event,
 		ret = machine__process_aux_event(machine, event); break;
 	case PERF_RECORD_ITRACE_START:
 		ret = machine__process_itrace_start_event(machine, event);
+	case PERF_RECORD_LOST_SAMPLES:
+		ret = machine__process_lost_samples_event(machine, event, sample); break;
 		break;
 	default:
 		ret = -1;
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index 1d99296..7ba5e8f 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -81,6 +81,8 @@ int machine__process_fork_event(struct machine *machine, union perf_event *event
 				struct perf_sample *sample);
 int machine__process_lost_event(struct machine *machine, union perf_event *event,
 				struct perf_sample *sample);
+int machine__process_lost_samples_event(struct machine *machine, union perf_event *event,
+					struct perf_sample *sample);
 int machine__process_aux_event(struct machine *machine,
 			       union perf_event *event);
 int machine__process_itrace_start_event(struct machine *machine,
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index e722107..4a5a609 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -325,6 +325,8 @@ void perf_tool__fill_defaults(struct perf_tool *tool)
 		tool->exit = process_event_stub;
 	if (tool->lost == NULL)
 		tool->lost = perf_event__process_lost;
+	if (tool->lost_samples == NULL)
+		tool->lost_samples = perf_event__process_lost_samples;
 	if (tool->aux == NULL)
 		tool->aux = perf_event__process_aux;
 	if (tool->itrace_start == NULL)
@@ -606,6 +608,7 @@ static perf_event__swap_op perf_event__swap_ops[] = {
 	[PERF_RECORD_SAMPLE]		  = perf_event__all64_swap,
 	[PERF_RECORD_AUX]		  = perf_event__aux_swap,
 	[PERF_RECORD_ITRACE_START]	  = perf_event__itrace_start_swap,
+	[PERF_RECORD_LOST_SAMPLES]	  = perf_event__all64_swap,
 	[PERF_RECORD_HEADER_ATTR]	  = perf_event__hdr_attr_swap,
 	[PERF_RECORD_HEADER_EVENT_TYPE]	  = perf_event__event_type_swap,
 	[PERF_RECORD_HEADER_TRACING_DATA] = perf_event__tracing_data_swap,
@@ -1049,6 +1052,10 @@ static int machines__deliver_event(struct machines *machines,
 		if (tool->lost == perf_event__process_lost)
 			evlist->stats.total_lost += event->lost.lost;
 		return tool->lost(tool, event, sample, machine);
+	case PERF_RECORD_LOST_SAMPLES:
+		if (tool->lost_samples == perf_event__process_lost_samples)
+			evlist->stats.total_lost_samples += event->lost_samples.lost;
+		return tool->lost_samples(tool, event, sample, machine);
 	case PERF_RECORD_READ:
 		return tool->read(tool, event, sample, evsel, machine);
 	case PERF_RECORD_THROTTLE:
@@ -1286,6 +1293,18 @@ static void perf_session__warn_about_errors(const struct perf_session *session)
 			    stats->nr_events[PERF_RECORD_LOST]);
 	}
 
+	if (session->tool->lost_samples == perf_event__process_lost_samples) {
+		double drop_rate;
+
+		drop_rate = (double)stats->total_lost_samples /
+			    (double) (stats->nr_events[PERF_RECORD_SAMPLE] + stats->total_lost_samples);
+		if (drop_rate > 0.05) {
+			ui__warning("Processed %lu samples and lost %3.2f%% samples!\n\n",
+				    stats->nr_events[PERF_RECORD_SAMPLE] + stats->total_lost_samples,
+				    drop_rate * 100.0);
+		}
+	}
+
 	if (stats->nr_unknown_events != 0) {
 		ui__warning("Found %u unknown events!\n\n"
 			    "Is this an older tool processing a perf.data "
diff --git a/tools/perf/util/tool.h b/tools/perf/util/tool.h
index 7f282ad..c307dd4 100644
--- a/tools/perf/util/tool.h
+++ b/tools/perf/util/tool.h
@@ -43,6 +43,7 @@ struct perf_tool {
 			fork,
 			exit,
 			lost,
+			lost_samples,
 			aux,
 			itrace_start,
 			throttle,
-- 
1.8.3.1

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