rtla/osnoise: Better report when histogram is empty

JIRA: https://issues.redhat.com/browse/RHEL-50869

commit 587f05a
Author: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Date:   Wed Jun 12 07:36:22 2024 -0300

    rtla/osnoise: Better report when histogram is empty

    When osnoise hist does not observe any samples above the threshold,
    no entries are recorded and the final report shows empty entries
    for the usual statistics (count, min, max, avg):

        [~]# osnoise hist -d 5s -T 500
        # RTLA osnoise histogram
        # Time unit is microseconds (us)
        # Duration:   0 00:00:05
        Index
        over:
        count:
        min:
        avg:
        max:

    That could lead users to confusing interpretations of the results.

    A simple solution is to report 0 for count and the statistics, making it
    clear that no noise (above the defined threshold) was observed:

        [~]# osnoise hist -d 5s -T 500
        # RTLA osnoise histogram
        # Time unit is microseconds (us)
        # Duration:   0 00:00:05
        Index
        over: 0
        count: 0
        min: 0
        avg: 0
        max: 0

    Link: https://lkml.kernel.org/r/Zml6JmH5cbS7-HfZ@uudg.org

    Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
    Cc: John Kacur <jkacur@redhat.com>
    Cc: Clark Williams <williams@redhat.com>
    Reviewed-by: John Kacur <jkacur@redhat.com>
    Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
    Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>

Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>

Author: lclaudio

tools/tracing/rtla/src/osnoise_hist.c

@@ -373,6 +373,7 @@ osnoise_print_stats(struct osnoise_hist_params *params, struct osnoise_tool *too
 {
 	struct osnoise_hist_data *data = tool->data;
 	struct trace_instance *trace = &tool->trace;
+	int has_samples = 0;
 	int bucket, cpu;
 	int total;
 
@@ -401,11 +402,25 @@ osnoise_print_stats(struct osnoise_hist_params *params, struct osnoise_tool *too
 			continue;
 		}
 
+		/* There are samples above the threshold */
+		has_samples = 1;
 		trace_seq_printf(trace->seq, "\n");
 		trace_seq_do_printf(trace->seq);
 		trace_seq_reset(trace->seq);
 	}
 
+	/*
+	 * If no samples were recorded, skip calculations, print zeroed statistics
+	 * and return.
+	 */
+	if (!has_samples) {
+		trace_seq_reset(trace->seq);
+		trace_seq_printf(trace->seq, "over: 0\ncount: 0\nmin: 0\navg: 0\nmax: 0\n");
+		trace_seq_do_printf(trace->seq);
+		trace_seq_reset(trace->seq);
+		return;
+	}
+
 	if (!params->no_index)
 		trace_seq_printf(trace->seq, "over: ");