Hi Steven, On Wed, Jul 15, 2020 at 10:36 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > To rule out that this may be an issue with the function_graph tracer, > can you also try it with: > > ftrace=function ftrace_filter=worqueue_prepare_cpu > > And see if the function tracer shows anything. > > /me just looked at the code. > > Yes, the function tracer is set up to trace really early, but the > function_graph tracer is initialized by core_initcall(), which is much > later. > > Perhaps try this patch (note, it's from latest mainline): > > And retry the function_graph tracer. With this patch, the function graph tracer doesn't work at boot time. Please see the log below: # mount -t debugfs debugfs /sys/kernel/debug/ # cd /sys/kernel/debug/tracing/trace # cat current_tracer nop Note that I tested it both on 5.4.47-rt28 and 5.6.19-rt11 (but not on latest mainline). Regarding the function tracer, you were correct: it can trace workqueue_prepare_cpu without any issue. Thank you, Itai Handler
