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

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Message-ID: <20080930181436.GA19690@Krystal>
Date:	Tue, 30 Sep 2008 14:14:36 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Martin Bligh <mbligh@...gle.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	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

* Martin Bligh (mbligh@...gle.com) wrote:
> On Tue, Sep 30, 2008 at 10:22 AM, Martin Bligh <mbligh@...gle.com> wrote:
> >> A 4 byte dataless payload is useless anyway.
> >
> > Not at all convinced that's true - we used it for lots of things.
> > Start and end of irq event is one frequent example.
> >
> > Also, in a compact mode, we can record start and end of
> > syscalls like this (without parameters).
> 
> Ah, sorry, maybe I misread this. No data with no event ids, etc
> is fairly useless. 4 bytes data including space to record event ids is OK.

In Steven's scheme, the event IDs in the 4 bytes are reserved for
(useless) internal use ;) They can therefore not be used for specific
tracer event IDs, which I think is a misuse of the precious bits
otherwise available to store really useful event IDs.

Mathieu

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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