linux-kernel - Re: [PATCH] tracing/markers: make markers select tracepoints

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Date:	Mon, 23 Feb 2009 12:11:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Frank Ch. Eigler" <fche@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, zippel@...ux-m68k.org,
	linux-kbuild@...r.kernel.org
Subject: Re: [PATCH] tracing/markers: make markers select tracepoints

On Sun, 2009-02-22 at 07:24 -0500, Frank Ch. Eigler wrote:
> Hi -
> 
> On Sun, Feb 22, 2009 at 01:14:36PM +0100, Peter Zijlstra wrote:
> > > > I would like to never merge an ftrace_printk() user... just as I'd like
> > > > to get rid of every marker.
> > > 
> > > But why?  They solve a problem well enough that Ingo had in effect
> > > reinvented them on Friday.
> > 
> > Because after a printk() debug spree, I don't commit them, I toss them
> > out and keep the fix.
> 
> Markers solve a problem closer to tracepoints than to debugging
> printk's.

Not so. In both cases the regular stuff (NMI trace, OOPS,
function/graph/sched trace, etc) is not enough and you wish to augment
its output.

> In this context, the main difference between tracepoints is that
> markers need almost no hand-written glue code of the sort that make up
> ftrace engines that just trace simple values.  Simpler & smaller code
> for the same output seems like a win.

Right, for dumb tracers that's true I suppose, however any
high-bandwidth tracer will try to avoid putting silly ASCII strings in
and will therefore need to write more glue code.

Which reduces these default thingies to printk() level debugging.

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