linux-kernel - Re: tracer_init

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Date:   Mon, 7 Dec 2020 14:47:13 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        kernel@...gutronix.de
Subject: Re: tracer_init_tracefs really slow

On Mon, 07 Dec 2020 17:24:58 +0100
Lucas Stach <l.stach@...gutronix.de> wrote:

> I would be happy to test a patch on our whimpy machines, though. :)

Let me know if this helps:

-- Steve

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 06134189e9a7..48aa5b6a7d15 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9062,7 +9062,10 @@ int tracing_init_dentry(void)
 extern struct trace_eval_map *__start_ftrace_eval_maps[];
 extern struct trace_eval_map *__stop_ftrace_eval_maps[];
 
-static void __init trace_eval_init(void)
+static struct workqueue_struct *eval_map_wq __initdata;
+struct work_struct eval_map_work __initdata;
+
+static void __init eval_map_work_func(struct work_struct *work)
 {
 	int len;
 
@@ -9070,6 +9073,34 @@ static void __init trace_eval_init(void)
 	trace_insert_eval_map(NULL, __start_ftrace_eval_maps, len);
 }
 
+static int __init trace_eval_init(void)
+{
+	INIT_WORK(&eval_map_work, eval_map_work_func);
+
+	eval_map_wq = alloc_workqueue("eval_map_wq", WQ_UNBOUND, 0);
+	if (!eval_map_wq) {
+		pr_err("Unable to allocate eval_map_wq\n");
+		/* Do work here */
+		eval_map_work_func(&eval_map_work);
+		return -ENOMEM;
+	}
+
+	queue_work(eval_map_wq, &eval_map_work);
+	return 0;
+}
+
+static int __init trace_eval_sync(void)
+{
+	/* Make sure the eval map updates are finished */
+	if (eval_map_wq)
+		destroy_workqueue(eval_map_wq);
+	return 0;
+}
+
+subsys_initcall(trace_eval_init);
+late_initcall_sync(trace_eval_sync);
+
+
 #ifdef CONFIG_MODULES
 static void trace_module_add_evals(struct module *mod)
 {
@@ -9171,8 +9202,6 @@ static __init int tracer_init_tracefs(void)
 	trace_create_file("saved_tgids", 0444, NULL,
 			NULL, &tracing_saved_tgids_fops);
 
-	trace_eval_init();
-
 	trace_create_eval_file(NULL);
 
 #ifdef CONFIG_MODULES