Re: [PATCH v4 5/5] blktrace: Make init_blk_tracer() asynchronous when trace_async_init set

[Steven Rostedt]

On Thu, 29 Jan 2026 22:26:08 -0500
Steven Rostedt <rost...@goodmis.org> wrote:

> Use trace_printk() instead. printk now has a "deferred" output. I'm not
> sure if the timestamps of when it prints is when the print took place
> or when it got to the console :-/

I added the below patch and have this result:

   kworker/u33:1-79      [002] .....     1.840855: trace_event_update_all: 
Start syncing
       swapper/0-1       [005] .....     6.045742: trace_eval_sync: sync maps
   kworker/u33:1-79      [002] .....    12.289296: trace_event_update_all: 
Finish syncing
       swapper/0-1       [005] .....    12.289387: trace_eval_sync: sync maps 
complete

Which shows that the final initcall waited for the work queue to complete:

-- Steve

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 396d59202438..33180d5622a8 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -10817,9 +10817,11 @@ subsys_initcall(trace_eval_init);
 
 static int __init trace_eval_sync(void)
 {
+       trace_printk("sync maps\n");
        /* Make sure the eval map updates are finished */
        if (eval_map_wq)
                destroy_workqueue(eval_map_wq);
+       trace_printk("sync maps complete\n");
        return 0;
 }
 
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index af6d1fe5cab7..194b344400e9 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -3555,6 +3555,7 @@ void trace_event_update_all(struct trace_eval_map **map, 
int len)
        int last_i;
        int i;
 
+       trace_printk("Start syncing\n");
        down_write(&trace_event_sem);
        list_for_each_entry_safe(call, p, &ftrace_events, list) {
                /* events are usually grouped together with systems */
@@ -3593,6 +3594,8 @@ void trace_event_update_all(struct trace_eval_map **map, 
int len)
                cond_resched();
        }
        up_write(&trace_event_sem);
+       msleep(10000);
+       trace_printk("Finish syncing\n");
 }
 
 static bool event_in_systems(struct trace_event_call *call,