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

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Date:   Thu, 02 Mar 2017 16:54:57 -0800
From:   Todd Brandt <todd.e.brandt@...ux.intel.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, todd.e.brandt@...el.com
Subject: Re: [PATCH] ftrace: add ftrace_graph_max_depth kernel parameter

On Thu, 2017-03-02 at 19:39 -0500, Steven Rostedt wrote:
> On Thu, 2 Mar 2017 19:38:27 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > 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/
thanks!

BTW I had one other question for you, is it possible to move the ftrace
module's initialization further up the queue? ATM it initializes at
about 600ms into boot, which is fine since most of the performance
issues are happening at 1000ms+. But eventually it might be nice to
trace some of the earlier init code.

> > 
> > -- 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.
> 
> I need to make a patch to update the old documentation to reflect this
> as well. But I'll do that another time.
> 
> -- Steve