rtla/timerlat: Fix histogram report when a cpu count is 0

On short runs it is possible to get no samples on a cpu, like this:

# rtla timerlat hist -u -T50

Index IRQ-001 Thr-001 Usr-001 IRQ-002 Thr-002 Usr-002
2 1 0 0 0 0 0
33 0 1 0 0 0 0
36 0 0 1 0 0 0
49 0 0 0 1 0 0
52 0 0 0 0 1 0
over: 0 0 0 0 0 0
count: 1 1 1 1 1 0
min: 2 33 36 49 52 18446744073709551615
avg: 2 33 36 49 52 -
max: 2 33 36 49 52 0
rtla timerlat hit stop tracing
IRQ handler delay: (exit from idle) 48.21 us (91.09 %)
IRQ latency: 49.11 us
Timerlat IRQ duration: 2.17 us (4.09 %)
Blocking thread: 1.01 us (1.90 %)
swapper/2:0 1.01 us
------------------------------------------------------------------------
Thread latency: 52.93 us (100%)

Max timerlat IRQ latency from idle: 49.11 us in cpu 2

Note, the value 18446744073709551615 is the same as ~0.

Fix this by reporting no results for the min, avg and max if the count
is 0.

Link: https://lkml.kernel.org/r/[e-mail]

Cc: [e-mail]
Fixes: 1eeb6328e8b3 ("rtla/timerlat: Add timerlat hist mode")
Suggested-by: Daniel Bristot de Oliveria <[e-mail]>
Signed-off-by: John Kacur <[e-mail]>
Signed-off-by: Daniel Bristot de Oliveira <[e-mail]>

tools/tracing/rtla/src/timerlat_hist.c

···
 		if (!data->hist[cpu].irq_count && !data->hist[cpu].thread_count)
 			continue;
 
-		if (!params->no_irq)
-			trace_seq_printf(trace->seq, "%9llu ",
-					data->hist[cpu].min_irq);
+		if (!params->no_irq) {
+			if (data->hist[cpu].irq_count)
+				trace_seq_printf(trace->seq, "%9llu ",
+						data->hist[cpu].min_irq);
+			else
+				trace_seq_printf(trace->seq, "        - ");
+		}
 
-		if (!params->no_thread)
-			trace_seq_printf(trace->seq, "%9llu ",
-					data->hist[cpu].min_thread);
+		if (!params->no_thread) {
+			if (data->hist[cpu].thread_count)
+				trace_seq_printf(trace->seq, "%9llu ",
+						data->hist[cpu].min_thread);
+			else
+				trace_seq_printf(trace->seq, "        - ");
+		}
 
-		if (params->user_hist)
-			trace_seq_printf(trace->seq, "%9llu ",
-					data->hist[cpu].min_user);
+		if (params->user_hist) {
+			if (data->hist[cpu].user_count)
+				trace_seq_printf(trace->seq, "%9llu ",
+						data->hist[cpu].min_user);
+			else
+				trace_seq_printf(trace->seq, "        - ");
+		}
 	}
 	trace_seq_printf(trace->seq, "\n");
 
···
 		if (!data->hist[cpu].irq_count && !data->hist[cpu].thread_count)
 			continue;
 
-		if (!params->no_irq)
-			trace_seq_printf(trace->seq, "%9llu ",
-					data->hist[cpu].max_irq);
+		if (!params->no_irq) {
+			if (data->hist[cpu].irq_count)
+				trace_seq_printf(trace->seq, "%9llu ",
+						 data->hist[cpu].max_irq);
+			else
+				trace_seq_printf(trace->seq, "        - ");
+		}
 
-		if (!params->no_thread)
-			trace_seq_printf(trace->seq, "%9llu ",
-					data->hist[cpu].max_thread);
+		if (!params->no_thread) {
+			if (data->hist[cpu].thread_count)
+				trace_seq_printf(trace->seq, "%9llu ",
+						data->hist[cpu].max_thread);
+			else
+				trace_seq_printf(trace->seq, "        - ");
+		}
 
-		if (params->user_hist)
-			trace_seq_printf(trace->seq, "%9llu ",
-					data->hist[cpu].max_user);
+		if (params->user_hist) {
+			if (data->hist[cpu].user_count)
+				trace_seq_printf(trace->seq, "%9llu ",
+						data->hist[cpu].max_user);
+			else
+				trace_seq_printf(trace->seq, "        - ");
+		}
 	}
 	trace_seq_printf(trace->seq, "\n");
 	trace_seq_do_printf(trace->seq);