linux-kernel - Re: [Patch] Tracing/ftrace: Adds a marker to allow user comments

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Message-ID: <20080828214256.296e34ec@daedalus.pq.iki.fi>
Date:	Thu, 28 Aug 2008 21:42:56 +0300
From:	Pekka Paalanen <pq@....fi>
To:	"Frédéric Weisbecker" <fweisbec@...il.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [Patch] Tracing/ftrace: Adds a marker to allow user comments

On Thu, 28 Aug 2008 11:04:36 +0100
"Frédéric Weisbecker" <fweisbec@...il.com> wrote:

> 2008/8/27 Pekka Paalanen <pq@....fi>:
> >
> > tracers. I would also like to be able to have e.g. mmiotrace_marker(),
> > which would have the same signature as ftrace_printk(), but is a no-op if
> > mmiotrace is not active. So, we could have an __ftrace_vprintk() to make
> > writing such wrappers easy. And the wrappers could be #ifdef'd away, if
> > the corresponding tracer is not built.
> 
> I like your idea of a ftrace_vprintk wrapper.
> But actually I'm questioning about the fact that the tracing api
> itself is not generic enough.

I think making it more modular would be nice, but I'm not really working
on the generic parts.

> And (always IMHO) I think that functions like __trace_mmiotrace_rw()
> shouldn't be located on trace.c but implemented on the appropriate
> tracer (in this example: trace_mmiotrace.c).

I feel the same.

> > I recall somewhere mentioning, that one shouldn't leave ftrace_printk's
> > lying around in "final" code, so I'm not sure how people feel about this
> > wrapping idea, especially when e.g. mmiotrace is hoped to be built-in by
> > default. OTOH, I don't think in-tree drivers and stuff want to use them,
> > so they would be mostly offered for out-of-tree modules
> > (reverse-engineering) and developers (debugging). That makes me wonder
> > if they would be accepted (as exported symbols).
> 
> Yes I think such a function should really be exported. For example
> using mmiotrace on a module and beeing able to signal the fact that we
> are entering the "foo" function seems to me very useful. It's
> important to know where we are in all these IO for debugging....

Yes, but the atmosphere is that if there are no users in-tree, the feature
gets kicked, out-of-tree users or no. That's the reason mmiotrace went
in-tree in the first place. So, to get that stuff exported, we might need
in-tree users, I believe.


Thanks.

-- 
Pekka Paalanen
http://www.iki.fi/pq/
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