linux-kernel - Re: [PATCH 3/4] tracing: Allow mmio tracer to display trace

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Message-ID: <20100513152915.3d3f852b@daedalus.pq.iki.fi>
Date:	Thu, 13 May 2010 15:29:15 +0300
From:	Pekka Paalanen <pq@....fi>
To:	rostedt@...dmis.org
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Larry Finger <Larry.Finger@...inger.net>
Subject: Re: [PATCH 3/4] tracing: Allow mmio tracer to display
 trace_printk() and other events

On Thu, 13 May 2010 08:15:09 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Thu, 2010-05-13 at 11:54 +0300, Pekka Paalanen wrote:
> > On Wed, 12 May 2010 21:21:13 -0400
> > Steven Rostedt <rostedt@...dmis.org> wrote:
> > 
> > > From: Steven Rostedt <srostedt@...hat.com>
> > > 
> > > The mmio tracer has its own function to handle reading of
> > > events. But if it encounters an event that it does not
> > > understand it ignores it instead of telling the calling
> > > function that it is not processing it.
> > > 
> > > If someone adds trace_printk() or enables events along with
> > > the mmio tracer, then these events will not be displayed in
> > > the trace output.
> > > 
> > > Simple solution is to just have the mmio print return
> > > UNHANDLED to let the caller know that it did not processes
> > > the event and the caller can process the event further.
> > 
> > Does this not mean that the mmiotrace output may contain
> > foreign lines? If it does, it will break the user space.
> > The dump format is specified in
> > Documentation/trace/mmiotrace.txt.
> > 
> > If you want to handle arbitrary messages, format them as
> > MARK events, please.
> > 
> > If I understood correctly, then NAK for this patch. Otherwise,
> > could you explain how this does not break the mmiotrace dump
> > format?
> > 
> > Is the tracing infrastructure now supporting several
> > active tracers at the same time? If yes, and if mmiotrace
> > should be able to co-operate, we need a new revision of the
> > dump format, or a tool that extracts the mmiotrace
> > events in the current format.
> > 
> 
> It only displays other events if the user enabled those events.
> 
> But that said, I don't want to break existing userspace tools. I
> can add a mmiotrace option "mmiotrace_all_events", if the user
> wants to see all events within the mmiotracer then they can just
> enable that option, otherwise, the mmiotracer will act like it
> currently does.
> 
> How does that sound?

That would be fine. Is it not redundant with what you said in
your first sentence?

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