linux-kernel - Re: [patch 0/4] perf_counter tools: support annotation of live kernel modules

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Date:	Fri, 03 Jul 2009 10:00:58 +0200
From:	Mike Galbraith <efault@....de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [patch 0/4] perf_counter tools: support annotation of live
 kernel modules

On Fri, 2009-07-03 at 09:29 +0200, Ingo Molnar wrote:
> * Mike Galbraith <efault@....de> wrote:
> 
> > On Thu, 2009-07-02 at 09:17 +0200, Mike Galbraith wrote:
> > 
> > > After I resurrect (well, try) live annotation in top...
> > 
> > Random thought wrt live top annotation: instead of resurrecting in 
> > the previous form, which could be a bit intrusive display space 
> > wise, what do you think of this idea?
> > 
> > Provide a kbd input snapshot trigger which builds a perf record 
> > (hard?) compatible file for the symbols being displayed.  Start a 
> > background task to annotate the lot, stuffing annotate output into 
> > an output file.
> > 
> > Better ideas highly welcome.
> 
> Hm, is there really a performance problem?

Sort of..

> We need to calculate and cache the objdump annotation output once, 
> but after that it should be pretty fast as we just display updated 
> counts with the same lines over and over again. No repeated objdump 
> runs are needed.

But active files follow symbols, which change on the fly.

Besides, as mentioned previously, while displayed annotation was very
cool, it took a lot of display space.  For me, top with the ability to
emit bic-disposable mini-reports would be my primary perf tools usage.
I'd only use big brothers when I needed their power/detail.

	-Mike

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