Move trace_eval_init() to subsys_initcall to make it start
earlier.
And to avoid tracer_init_tracefs being blocked by
trace_event_sem which trace_eval_init() hold [1],
queue tracer_init_tracefs() to eval_map_wq to let
the two works being executed sequentially.

It can speed up the initialization of kernel as result
of making tracer_init_tracefs asynchronous.

On my arm64 platform, it reduce ~20ms of 125ms which total
time do_initcalls spend.

[1]: https://lore.kernel.org/r/68d7b3327052757d0cd6359a6c9015a85b437232.camel@pengutronix.de
Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
---
 kernel/trace/trace.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 85ec758c4455..2974ae056068 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9571,6 +9571,7 @@ extern struct trace_eval_map *__stop_ftrace_eval_maps[];
 
 static struct workqueue_struct *eval_map_wq __initdata;
 static struct work_struct eval_map_work __initdata;
+static struct work_struct tracerfs_init_work __initdata;
 
 static void __init eval_map_work_func(struct work_struct *work)
 {
@@ -9596,6 +9597,8 @@ static int __init trace_eval_init(void)
 	return 0;
 }
 
+subsys_initcall(trace_eval_init);
+
 static int __init trace_eval_sync(void)
 {
 	/* Make sure the eval map updates are finished */
@@ -9678,15 +9681,8 @@ static struct notifier_block trace_module_nb = {
 };
 #endif /* CONFIG_MODULES */
 
-static __init int tracer_init_tracefs(void)
+static __init void tracer_init_tracefs_work_func(struct work_struct *work)
 {
-	int ret;
-
-	trace_access_lock_init();
-
-	ret = tracing_init_dentry();
-	if (ret)
-		return 0;
 
 	event_trace_init();
 
@@ -9708,8 +9704,6 @@ static __init int tracer_init_tracefs(void)
 	trace_create_file("saved_tgids", TRACE_MODE_READ, NULL,
 			NULL, &tracing_saved_tgids_fops);
 
-	trace_eval_init();
-
 	trace_create_eval_file(NULL);
 
 #ifdef CONFIG_MODULES
@@ -9724,6 +9718,23 @@ static __init int tracer_init_tracefs(void)
 	create_trace_instances(NULL);
 
 	update_tracer_options(&global_trace);
+}
+
+static __init int tracer_init_tracefs(void)
+{
+	int ret;
+
+	trace_access_lock_init();
+
+	ret = tracing_init_dentry();
+	if (ret)
+		return 0;
+
+	INIT_WORK(&tracerfs_init_work, tracer_init_tracefs_work_func);
+	if (!eval_map_wq)
+		tracer_init_tracefs_work_func(&tracerfs_init_work);
+	else
+		queue_work(eval_map_wq, &tracerfs_init_work);
 
 	return 0;
 }
-- 
2.18.0

On Wed, 23 Mar 2022 23:22:57 +0800
Mark-PK Tsai <mark-pk.tsai@mediatek.com> wrote:

> +static __init int tracer_init_tracefs(void)
> +{
> +	int ret;
> +
> +	trace_access_lock_init();
> +
> +	ret = tracing_init_dentry();
> +	if (ret)
> +		return 0;
> +
> +	INIT_WORK(&tracerfs_init_work, tracer_init_tracefs_work_func);
> +	if (!eval_map_wq)
> +		tracer_init_tracefs_work_func(&tracerfs_init_work);

Why go through the bother of doing the INIT_WORK if eval_map_wq is not
created? Just do:

	if (eval_map_wq) {
		INIT_WORK(&tracerfs_init_work, tracer_init_tracefs_work_func);
		queue_work(eval_map_wq, &tracerfs_init_work);
	} else {
		tracer_init_tracefs_work_func(NULL);
	}

But that's just a nit anyway.

-- Steve



> +	else
> +		queue_work(eval_map_wq, &tracerfs_init_work);
>  
>  	return 0;
>  }

> > +static __init int tracer_init_tracefs(void)
> > +{
> > +	int ret;
> > +
> > +	trace_access_lock_init();
> > +
> > +	ret = tracing_init_dentry();
> > +	if (ret)
> > +		return 0;
> > +
> > +	INIT_WORK(&tracerfs_init_work, tracer_init_tracefs_work_func);
> > +	if (!eval_map_wq)
> > +		tracer_init_tracefs_work_func(&tracerfs_init_work);
> 
> Why go through the bother of doing the INIT_WORK if eval_map_wq is not
> created? Just do:
> 
> 	if (eval_map_wq) {
> 		INIT_WORK(&tracerfs_init_work, tracer_init_tracefs_work_func);
> 		queue_work(eval_map_wq, &tracerfs_init_work);
> 	} else {
> 		tracer_init_tracefs_work_func(NULL);
> 	}

Got it, I will update it in v4.
Thanks!

> 
> But that's just a nit anyway.
> 
> -- Steve
> 
> 
> 
> > +	else
> > +		queue_work(eval_map_wq, &tracerfs_init_work);
> >  
> >  	return 0;
> >  }