linux-kernel - [PATCH V2 2/3] tracing/osnoise: Skip running osnoise if all instances are off

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Message-Id: <68d78e1f3bdedd75119c10626ecdfd0580111cb9.1684860626.git.bristot@kernel.org>
Date:   Tue, 23 May 2023 19:22:47 +0200
From:   Daniel Bristot de Oliveira <bristot@...nel.org>
To:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Juri Lelli <juri.lelli@...hat.com>,
        William White <chwhite@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jonathan Corbet <corbet@....net>
Subject: [PATCH V2 2/3] tracing/osnoise: Skip running osnoise if all instances are off

In the case of all tracing instances being off, sleep for the entire
period.

 Q: Why not kill all threads so?
 A: It is valid and useful to start the threads with tracing off.
For example, rtla disables tracing, starts the tracer, applies the
scheduling setup to the threads, e.g., sched priority and cgroup,
and then begin tracing with all set.

Skipping the period helps to speed up rtla setup and save the
trace after a stop tracing.

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Daniel Bristot de Oliveira <bristot@...nel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Jonathan Corbet <corbet@....net>
Signed-off-by: Daniel Bristot de Oliveira <bristot@...nel.org>
---
 kernel/trace/trace_osnoise.c | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index c265ec5f1726..220172cb874d 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1285,6 +1285,22 @@ static __always_inline void osnoise_stop_tracing(void)
 	rcu_read_unlock();
 }
 
+/*
+ * osnoise_has_tracing_on - Check if there is at least one instance on
+ */
+static __always_inline int osnoise_has_tracing_on(void)
+{
+	struct osnoise_instance *inst;
+	int trace_is_on = 0;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(inst, &osnoise_instances, list)
+		trace_is_on += tracer_tracing_is_on(inst->tr);
+	rcu_read_unlock();
+
+	return trace_is_on;
+}
+
 /*
  * notify_new_max_latency - Notify a new max latency via fsnotify interface.
  */
@@ -1517,13 +1533,16 @@ static struct cpumask save_cpumask;
 /*
  * osnoise_sleep - sleep until the next period
  */
-static void osnoise_sleep(void)
+static void osnoise_sleep(bool skip_period)
 {
 	u64 interval;
 	ktime_t wake_time;
 
 	mutex_lock(&interface_lock);
-	interval = osnoise_data.sample_period - osnoise_data.sample_runtime;
+	if (skip_period)
+		interval = osnoise_data.sample_period;
+	else
+		interval = osnoise_data.sample_period - osnoise_data.sample_runtime;
 	mutex_unlock(&interface_lock);
 
 	/*
@@ -1604,8 +1623,14 @@ static int osnoise_main(void *data)
 		if (osnoise_migration_pending())
 			break;
 
+		/* skip a period if tracing is off on all instances */
+		if (!osnoise_has_tracing_on()) {
+			osnoise_sleep(true);
+			continue;
+		}
+
 		run_osnoise();
-		osnoise_sleep();
+		osnoise_sleep(false);
 	}
 
 	migrate_enable();
-- 
2.38.1