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>

diff --git a/tools/tracing/rtla/src/osnoise_hist.c b/tools/tracing/rtla/src/osnoise_hist.c
index 7be17d09f7e8567ef61c28c78c121cecd8bb2198..214e2c93fde0166aa92b76d2e6b0b81fe3b76c1a 100644 (file)
--- a/tools/tracing/rtla/src/osnoise_hist.c
+++ b/tools/tracing/rtla/src/osnoise_hist.c
@@ -374,6 +374,7 @@ 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;
 
@@ -402,11 +403,25 @@ 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: ");