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

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Date:	Tue, 30 Sep 2008 13:49:48 -0700
From:	"Martin Bligh" <mbligh@...gle.com>
To:	"Mathieu Desnoyers" <mathieu.desnoyers@...ymtl.ca>
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

> I am not saying anything about the actual number of events with 0 bytes
> payload I actually have in my own instrumentation, if this is what you
> mean. I am just saying that it leaves this room available for such
> events.

It would, yes. Are they useful?

> Even if there is a 32 bits payload associated with those events, the
> fact that we can encode the event ID in the 32 bits header will bring
> those events from 96 bits (due to 32 bits alignment) down to 64 bits.

That's true. So do we have a bunch of stuff that we really really need
that'd fit into 32 bits, but not 28 bits?

>> This is all over 1 bit of information, right? Since you need at least 1 for
>> the timestamp stuff.
>
> 4 bits of information could be added to the 32-bits header if we allow
> tracers to register their first 15 event IDs in those 4 bits.
>
> But well... let's keep that for v2. ;)

Sounds like a plan ;-) All this stuff is internal representations anyway.
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