linux-kernel - [for-next][PATCH 2/3] rtla/osnoise: Better report when histogram is empty

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Date: Thu, 27 Jun 2024 16:50:24 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org
Cc: Daniel Wagner <dwagner@...e.de>,
 "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>,
 Clark Williams <williams@...hat.com>,
 Daniel Bristot de Oliveira <bristot@...nel.org>,
 John Kacur <jkacur@...hat.com>
Subject: [for-next][PATCH 2/3] rtla/osnoise: Better report when histogram is empty

From: "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>

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@...nel.org>
Cc: John Kacur <jkacur@...hat.com>
Cc: Clark Williams <williams@...hat.com>
Reviewed-by: John Kacur <jkacur@...hat.com>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@...hat.com>
Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
---
 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 7be17d09f7e8..214e2c93fde0 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: ");
 
-- 
2.43.0