linux-kernel - Re: [PATCH] ftrace: Document that multiple function

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Message-ID: <20250114104716.74c9b389@gandalf.local.home>
Date: Tue, 14 Jan 2025 10:47:16 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
 <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH] ftrace: Document that multiple function_graph tracing
 may have different times

On Tue, 14 Jan 2025 10:12:02 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <rostedt@...dmis.org>
> 
> The function graph tracer now calculates the calltime internally and for
> each instance. If there are two instances that are running function graph
> tracer and are tracing the same functions, the timings of the length of
> those functions may be slightly different:
> 
>  # trace-cmd record -B foo -p function_graph -B bar -p function_graph sleep 5
>  # trace-cmd report
> [..]
> bar:            sleep-981   [000] ...1.  1101.109027: funcgraph_entry:        0.764 us   |          mutex_unlock(); (ret=0xffff8abcc256c300)
> foo:            sleep-981   [000] ...1.  1101.109028: funcgraph_entry:        0.748 us   |          mutex_unlock(); (ret=0xffff8abcc256c300)
> bar:            sleep-981   [000] .....  1101.109029: funcgraph_exit:         2.456 us   |        } (ret=0xffff8abcc256c300)
> foo:            sleep-981   [000] .....  1101.109029: funcgraph_exit:         2.403 us   |        } (ret=0xffff8abcc256c300)
> bar:            sleep-981   [000] d..1.  1101.109031: funcgraph_entry:        0.844 us   |  fpregs_assert_state_consistent(); (ret=0x0)
> foo:            sleep-981   [000] d..1.  1101.109032: funcgraph_entry:        0.803 us   |  fpregs_assert_state_consistent(); (ret=0x0)
> 

I added:

  Link: https://lore.kernel.org/all/20250114101806.b2778cb01f34f5be9d23ad98@kernel.org/
 
  Suggested-by: Masami Hiramatsu <mhiramat@...nel.org>

To this as well.

-- Steve

> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  Documentation/trace/ftrace.rst | 6 ++++++
>  1 file changed, 6 insertions(+)