linux-kernel - Re: [PATCH] ftrace: add ftrace_graph_max

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Date:   Thu, 2 Mar 2017 19:38:27 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Todd Brandt <todd.e.brandt@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, todd.e.brandt@...el.com
Subject: Re: [PATCH] ftrace: add ftrace_graph_max_depth kernel parameter

On Thu,  2 Mar 2017 16:12:15 -0800
Todd Brandt <todd.e.brandt@...ux.intel.com> wrote:

> Early trace callgraphs can be extremely large on systems with
> several seconds of boot time. The max_depth parameter limits how
> deep the graph trace goes and reduces the output size. This
> parameter is the same as the max_graph_depth file in debugfs.

I'll take this with one modification I'll make. s/debugfs/tracefs/
because it's really the tracefs file system now. It just happens to be
automatically mounted in the debugfs file system. But can be by itself
in /sys/kernel/tracing/

-- Steve

> 
> Signed-off-by: Todd Brandt <todd.e.brandt@...ux.intel.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
>  kernel/trace/ftrace.c                           | 9 +++++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 986e443..1a8575f 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1183,6 +1183,12 @@
>  			functions that can be changed at run time by the
>  			set_graph_notrace file in the debugfs tracing directory.
>  
> +	ftrace_graph_max_depth=<uint>
> +			[FTRACE] Used with the function graph tracer. This is
> +			the max depth it will trace into a function. This value
> +			can be changed at run time by the max_graph_depth file
> +			in the debugfs tracing directory. default: 0 (no limit)
> +
>  	gamecon.map[2|3]=
>  			[HW,JOY] Multisystem joystick and NES/SNES/PSX pad
>  			support via parallel port (up to 5 devices per port)
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 0c06093..fc6b024 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -4415,6 +4415,15 @@ static int __init set_graph_notrace_function(char *str)
>  }
>  __setup("ftrace_graph_notrace=", set_graph_notrace_function);
>  
> +static int __init set_graph_max_depth_function(char *str)
> +{
> +	if (!str)
> +		return 0;
> +	fgraph_max_depth = simple_strtoul(str, NULL, 0);
> +	return 1;
> +}
> +__setup("ftrace_graph_max_depth=", set_graph_max_depth_function);
> +
>  static void __init set_ftrace_early_graph(char *buf, int enable)
>  {
>  	int ret;