perf top: Drop samples which are behind the refresh rate

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.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/n/tip-x533ra5c1pgofvbtsizzuydd@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

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);