[PATCH 53/75] perf top: Drop samples which are behind the refresh rate

[Arnaldo Carvalho de Melo]

From: Jiri Olsa <jolsa@xxxxxxxxxx>

Drop samples from processing thread if they get behind the latest event
read from the kernel maps. If it gets behind more than the refresh rate
(-d option), drop the sample.

Acked-by: David S. Miller <davem@xxxxxxxxxxxxx>
Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/n/tip-x533ra5c1pgofvbtsizzuydd@xxxxxxxxxxxxxx
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/builtin-top.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 50ec01eb7f57..234232d538c2 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -833,6 +833,8 @@ perf_top__process_lost_samples(struct perf_top *top,
 	hists->stats.total_lost_samples += event->lost_samples.lost;
 }
 
+static u64 last_timestamp;
+
 static void perf_top__mmap_read_idx(struct perf_top *top, int idx)
 {
 	struct record_opts *opts = &top->record_opts;
@@ -845,14 +847,13 @@ static void perf_top__mmap_read_idx(struct perf_top *top, int idx)
 		return;
 
 	while ((event = perf_mmap__read_event(md)) != NULL) {
-		u64 timestamp = -1ULL;
 		int ret;
 
-		ret = perf_evlist__parse_sample_timestamp(evlist, event, &timestamp);
+		ret = perf_evlist__parse_sample_timestamp(evlist, event, &last_timestamp);
 		if (ret && ret != -1)
 			break;
 
-		ret = ordered_events__queue(top->qe.in, event, timestamp, 0);
+		ret = ordered_events__queue(top->qe.in, event, last_timestamp, 0);
 		if (ret)
 			break;
 
@@ -1084,6 +1085,21 @@ static void *process_thread(void *arg)
 	return NULL;
 }
 
+/*
+ * Allow only 'top->delay_secs' seconds behind samples.
+ */
+static int should_drop(struct ordered_event *qevent, struct perf_top *top)
+{
+	union perf_event *event = qevent->event;
+	u64 delay_timestamp;
+
+	if (event->header.type != PERF_RECORD_SAMPLE)
+		return false;
+
+	delay_timestamp = qevent->timestamp + top->delay_secs * NSEC_PER_SEC;
+	return delay_timestamp < last_timestamp;
+}
+
 static int deliver_event(struct ordered_events *qe,
 			 struct ordered_event *qevent)
 {
@@ -1096,6 +1112,9 @@ static int deliver_event(struct ordered_events *qe,
 	struct machine *machine;
 	int ret = -1;
 
+	if (should_drop(qevent, top))
+		return 0;
+
 	ret = perf_evlist__parse_sample(evlist, event, &sample);
 	if (ret) {
 		pr_err("Can't parse sample, err = %d\n", ret);
-- 
2.19.2