linux-kernel - [PATCH] rtla/osnoise: Better report when histogram is empty

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Date: Wed, 12 Jun 2024 07:36:22 -0300
From: "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>
To: Daniel Bristot de Oliveira <bristot@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Kacur <jkacur@...hat.com>,
	Clark Williams <williams@...hat.com>,
	linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] 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


Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@...hat.com>
---
 tools/tracing/rtla/src/osnoise_hist.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/tracing/rtla/src/osnoise_hist.c b/tools/tracing/rtla/src/osnoise_hist.c
index 7be17d09f7e85..214e2c93fde01 100644
--- 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: ");