linux-kernel - Re: [PATCH 0/2] ftrace: updates to tip

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Date:	Fri, 16 Jan 2009 12:23:45 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Chris Mason <chris.mason@...cle.com>
Subject: Re: [PATCH 0/2] ftrace: updates to tip


* Steven Rostedt <rostedt@...dmis.org> wrote:

> Ingo,
> 
> The first patch is critical, and needs to stay with trace_output.c Not 
> that critical since trace_output.c is not in mainline yet.
> 
> The second patch gives the ability to stack trace functions. I've been 
> leery about adding this and still keep it a separate option from the 
> "stacktrace" that already exists. This is because when enabled with no 
> filtering, the lag between typing and seeing what is typed can be up to 
> 10 seconds or more.

Btw., is this true even if frame pointers are enabled? When frame pointers 
are disabled we scan the full kernel stack => that can be quite slow if 
every kernel function is traced ;-)

> I made the function stack trace an option attached to the function 
> tracer, so it must be enabled after the function tracer has been set. 
> This still needs to be updated in ftrace.txt.

maybe we could drive this via the filter API? Something like:

   echo "*btrfs*:stacktrace" >> set_filter_functions

Would automatically mean that those functions will all generate 
stacktraces too. Note how safe this API is by default: the filter is used 
for a narrow scope of functions anwyay. To get it for all kernel functions 
one would have to do:

   echo "*:stacktrace" >> set_filter_functions

Which one cannot do accidentally.

What do you think?

> The following patches are in:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
> 
>     branch: tip/devel
> 
> 
> Lai Jiangshan (1):
>       ftrace: fix trace_output
> 
> Steven Rostedt (1):
>       ftrace: add stack trace to function tracer
> 
> ----
>  kernel/trace/trace.c           |   26 ++++++++----
>  kernel/trace/trace.h           |    7 +++
>  kernel/trace/trace_functions.c |   84 ++++++++++++++++++++++++++++++++++++++++
>  kernel/trace/trace_output.c    |   65 +++++++++++++++----------------
>  kernel/trace/trace_output.h    |    4 +-
>  5 files changed, 141 insertions(+), 45 deletions(-)

Pulled into tip/tracing/ftrace, thanks Steve!

	Ingo
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