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

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Date:	Thu, 13 May 2010 11:11:23 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Pekka Paalanen <pq@....fi>
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, 2010-05-13 at 15:29 +0300, Pekka Paalanen wrote:
> On Thu, 13 May 2010 08:15:09 -0400

> > 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?
> 

Right now with this patch as is. When you enable the mmiotracer it
clears the ring buffer. But if someone previously enabled an event (like
sched_switch for example) then that event will appear in the output of
the tracer.

The user will need to disable that event and restart the mmiotracer so
the output will not break the userspace tools. Is this OK?

If not, then my suggestion is to have an mmiotracer option that keeps it
from printing out any event except for the ones it knows about.

The reason I added this patch in the first place was because Larry
Finger was using the mmiotrace with trace_printk() and the current code
does not print out the trace_printk() when mmiotracer is active.

-- Steve

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