linux-kernel - Re: [RFC PATCH] LTTng relay buffer allocation, read, write

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Date:	Tue, 30 Sep 2008 16:21:14 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Frank Ch. Eigler" <fche@...hat.com>
cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Martin Bligh <mbligh@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, prasad@...ux.vnet.ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>, od@...e.com,
	Andrew Morton <akpm@...ux-foundation.org>, hch@....de,
	David Wilder <dwilder@...ibm.com>,
	Tom Zanussi <zanussi@...cast.net>
Subject: Re: [RFC PATCH] LTTng relay buffer allocation, read, write


On Tue, 30 Sep 2008, Frank Ch. Eigler wrote:
> On Tue, Sep 30, 2008 at 03:43:45PM -0400, Steven Rostedt wrote:
> > [...]
> > On Tue, 30 Sep 2008, Mathieu Desnoyers wrote:
> > > 
> > > You are actually using them to put redundant information that could be
> > > encoded differently and thus save 4 bits per event records, more or less
> > > what will be needed by most tracers (15 IDs, 1 reserved for an extended
> > > ID field).
> > 
> > I really like the idea of keeping the tracer event ids out of the ring 
> > buffer logic.
> 
> That's fine for a ring buffer that only ever contains data from one
> event source.  How do you imagine multiplexing working, where one
> wants to grep a single debugfs file that contains data from different
> event sources?  Punt to another layer?

Field goal!

Yes! That is exactly what I want. If your trace has only one event, why 
would it want to record them?  The event id belongs in the tracer layer 
not the ring buffer layer.

I would like to make a "trace_buffer" layer that includes all of this.

-- Steve

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