Use maximum over all traces for queue depth

So far we used maximum of the first trace for the maximum range of the
queue depth graph. Use maximum over all traces similarly as for other
line graphs.

Signed-off-by: Jan Kara <jack@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/iowatcher/main.c b/iowatcher/main.c
index cbe9155..b13f509 100644
--- a/iowatcher/main.c
+++ b/iowatcher/main.c
@@ -991,6 +991,7 @@
 			     unsigned int max_seconds)
 {
 	struct trace_file *tf;
+	u64 max = 0, val;
 
 	if (active_graphs[QUEUE_DEPTH_GRAPH_INDEX] == 0)
 		return;
@@ -1000,9 +1001,17 @@
 	if (num_traces > 1)
 		svg_alloc_legend(plot, num_traces);
 
-	tf = list_entry(all_traces.next, struct trace_file, list);
+	list_for_each_entry(tf, &all_traces, list) {
+		val = line_graph_roll_avg_max(tf->queue_depth_gld);
+		if (val > max)
+			max = val;
+	}
+
+	list_for_each_entry(tf, &all_traces, list)
+		tf->queue_depth_gld->max = max;
+
 	set_ylabel(plot, "Pending IO");
-	set_yticks(plot, num_yticks, 0, tf->queue_depth_gld->max, "");
+	set_yticks(plot, num_yticks, 0, max, "");
 	set_xticks(plot, num_xticks, min_seconds, max_seconds);
 
 	list_for_each_entry(tf, &all_traces, list) {