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

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Message-ID: <alpine.DEB.1.10.0809301541120.7993@gandalf.stny.rr.com>
Date:	Tue, 30 Sep 2008 15:43:45 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	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,
	"Frank Ch. Eigler" <fche@...hat.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, 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.

> 
> So the fact that you use them does not mean they are really required,
> and I don't think such duplicated information actually makes things more
> solid. Maybe just more obscure ?

Well, at least for version 1 these bits stay. I already found two bugs by 
hitting the event padding when the size said it should not have. This 
redundant information makes me feel a bit more cozy when they match.

-- Steve

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