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Date:   Tue, 14 Jul 2020 10:34:43 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Itai Handler <itai.handler@gmail.com>
Cc:     linux-rt-users@vger.kernel.org
Subject: Re: aarch64 boot time increases with rt
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On Tue, 14 Jul 2020 15:18:01 +0300
Itai Handler <itai.handler@gmail.com> wrote:

> I tried "ftrace=function_graph ftrace_graph_filter=workqueue_prepare_cpu",
> however, the trace appears to be empty.
> The function workqueue_prepare_cpu is not defined inline nor notrace.
> 
> Please see log below:
> # mount -t debugfs none /sys/kernel/debug
> # cd /sys/kernel/debug/tracing/
> # cat trace
> # tracer: function_graph
> #
> # CPU  DURATION                  FUNCTION CALLS
> # |     |   |                     |   |   |   |
> # cat set_graph_function
> workqueue_prepare_cpu
> # cat tracing_on
> 1
> 
> Do you have any idea why it's empty?

Hmm, does the place in question happen before ftrace is initialized?

That is, where do you see the message that has something like this:

 ftrace: allocating 41803 entries in 164 pages
 ftrace: allocated 164 pages with 3 groups

-- Steve