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

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Date:	Fri, 16 Jan 2009 14:08:36 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Steven Rostedt" <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Chris Mason" <chris.mason@...cle.com>
Subject: Re: [PATCH 0/2] ftrace: updates to tip

2009/1/16 Ingo Molnar <mingo@...e.hu>:
>
> * 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 ;-)


Hi Ingo,

The function tracer selects Frame pointers :-)

Frederic.


>> 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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