linux-kernel - Re: [PATCH 1/2] tracing/function-graph-tracer: signal interrupts entry/exit points on outpout

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Date:	Mon, 8 Dec 2008 14:47:36 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frédéric Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] tracing/function-graph-tracer: signal interrupts
	entry/exit points on outpout


* Frédéric Weisbecker <fweisbec@...il.com> wrote:

> 2008/12/8 Peter Zijlstra <a.p.zijlstra@...llo.nl>:
> > On Mon, 2008-12-08 at 01:54 +0100, Frederic Weisbecker wrote:
> >> Impact: provide interrupt detection on output
> >>
> >> Suggested by Ingo.
> >> If a hardirq is raised, we want it to be signaled on output, so this patch
> >> adds two arrows on the output to find entry and exit points of a hardirq.
> >>
> >> Unfortunately, there are many interrupt entrypoints and these can be differents
> >> from one arch to another.
> >>
> >> The approach here is one of the easiest, but doesn't shine by its scalability:
> >> we have an array of the interrupt entrypoints names that we compare with the
> >> symbol of the current traced function, if it matches, we draw the arrow.
> >>
> >> Ie:
> >>
> >>  1)               |                                unlock_buffer() {
> >>  1)               |                                  wake_up_bit() {
> >>  1)               |                                    bit_waitqueue() {
> >>  1)   0.872 us    |                                      __phys_addr();
> >>  1)   2.722 us    |                                    }
> >>  1)               |                                    __wake_up_bit() {
> >>  1)              ==>                                   __wake_up_bit() {
> >>  1)               |                                      do_IRQ() {
> >
> > Would be much nicer, the current proposal is lost when grepping and adds
> > a weird visual break in the output.
> 
> 
> Ok, I will apply it like this in the V2.
> Thanks!

note that since the IRQ marker always comes on an entry record, there's 
space in the usecs field for something like:

  1)   2.722 us    |                                    }
  1)               |                                    __wake_up_bit() {
  1)  [IRQ#123]   ==>                                   __wake_up_bit() {

right?

	Ingo
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