rtla/hwnoise: Reduce runtime to 75%

osnoise runs 100% of time by default. It makes sense because osnoise
is preemptive. hwnoise checks preemption once a second, so it
reduces system progress.

Reduce runtime to 75% to avoid problems by default. I added a Fixes
as it might avoid problems for first time users as it lands on distros.

Link: https://lkml.kernel.org/r/af0b7113ffc00031b9af4bb40ef5889a27dadf8c.1686066600.git.bristot@kernel.org

Cc: William White <chwhite@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Fixes: 1f42835 ("rtla: Add hwnoise tool")
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

tools/tracing/rtla/src/osnoise_top.c

@@ -348,8 +348,14 @@ struct osnoise_top_params *osnoise_top_parse_args(int argc, char **argv)
 	if (!params)
 		exit(1);
 
-	if (strcmp(argv[0], "hwnoise") == 0)
+	if (strcmp(argv[0], "hwnoise") == 0) {
 		params->mode = MODE_HWNOISE;
+		/*
+		 * Reduce CPU usage for 75% to avoid killing the system.
+		 */
+		params->runtime = 750000;
+		params->period = 1000000;
+	}
 
 	while (1) {
 		static struct option long_options[] = {