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

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Message-ID: <20080930200112.GD27822@redhat.com>
Date:	Tue, 30 Sep 2008 16:01:12 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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

Hi -

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?

- FChE
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