perf intel-pt: Tidy old_buffer handling in intel_pt_get_trace()

intel_pt_get_trace() fixes overlaps between the current buffer and the
previous buffer ('old_buffer').

However the previous buffer might not have had usable data (no PSB) so
the comparison must be made against the previous buffer that had usable
data.

Tidy that by keeping a pointer for that purpose in struct intel_pt_queue.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1520431349-30689-8-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/intel-pt.c

@@ -132,6 +132,7 @@ struct intel_pt_queue {
 	struct intel_pt *pt;
 	unsigned int queue_nr;
 	struct auxtrace_buffer *buffer;
+	struct auxtrace_buffer *old_buffer;
 	void *decoder;
 	const struct intel_pt_state *state;
 	struct ip_callchain *chain;
@@ -226,7 +227,8 @@ static int intel_pt_do_fix_overlap(struct intel_pt *pt, struct auxtrace_buffer *
 static int intel_pt_get_trace(struct intel_pt_buffer *b, void *data)
 {
 	struct intel_pt_queue *ptq = data;
-	struct auxtrace_buffer *buffer = ptq->buffer, *old_buffer = buffer;
+	struct auxtrace_buffer *buffer = ptq->buffer;
+	struct auxtrace_buffer *old_buffer = ptq->old_buffer;
 	struct auxtrace_queue *queue;
 
 	if (ptq->stop) {
@@ -235,7 +237,7 @@ static int intel_pt_get_trace(struct intel_pt_buffer *b, void *data)
 	}
 
 	queue = &ptq->pt->queues.queue_array[ptq->queue_nr];
-next:
+
 	buffer = auxtrace_buffer__next(queue, buffer);
 	if (!buffer) {
 		if (old_buffer)
@@ -267,16 +269,6 @@ static int intel_pt_get_trace(struct intel_pt_buffer *b, void *data)
 	}
 	b->ref_timestamp = buffer->reference;
 
-	/*
-	 * If in snapshot mode and the buffer has no usable data, get next
-	 * buffer and again check overlap against old_buffer.
-	 */
-	if (ptq->pt->snapshot_mode && !b->len)
-		goto next;
-
-	if (old_buffer)
-		auxtrace_buffer__drop_data(old_buffer);
-
 	if (!old_buffer || ptq->pt->sampling_mode || (ptq->pt->snapshot_mode &&
 						      !buffer->consecutive)) {
 		b->consecutive = false;
@@ -288,8 +280,14 @@ static int intel_pt_get_trace(struct intel_pt_buffer *b, void *data)
 	if (ptq->step_through_buffers)
 		ptq->stop = true;
 
-	if (!b->len)
+	if (b->len) {
+		if (old_buffer)
+			auxtrace_buffer__drop_data(old_buffer);
+		ptq->old_buffer = buffer;
+	} else {
+		auxtrace_buffer__drop_data(buffer);
 		return intel_pt_get_trace(b, data);
+	}
 
 	return 0;
 }