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/20240510190318.44295-1-jkacur@redhat.com

Cc: stable@vger.kernel.org
Fixes: 1eeb6328 ("rtla/timerlat: Add timerlat hist mode")
Suggested-by: Daniel Bristot de Oliveria <bristot@kernel.org>
Signed-off-by: John Kacur <jkacur@redhat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>

tools/tracing/rtla/src/timerlat_hist.c

@@ -327,17 +327,29 @@ timerlat_print_summary(struct timerlat_hist_params *params,
 		if (!data->hist[cpu].irq_count && !data->hist[cpu].thread_count)
 			continue;
 
-		if (!params->no_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)
+		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)
+		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");
 
@@ -387,17 +399,29 @@ timerlat_print_summary(struct timerlat_hist_params *params,
 		if (!data->hist[cpu].irq_count && !data->hist[cpu].thread_count)
 			continue;
 
-		if (!params->no_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)
+		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)
+		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);