linux-kernel - Re: [RFC PATCH 1/3] Unified trace buffer

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Message-ID: <alpine.LFD.1.10.0809251112580.3265@nehalem.linux-foundation.org>
Date:	Thu, 25 Sep 2008 11:14:57 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Martin Bligh <mbligh@...igh.org>,
	Martin Bligh <mbligh@...gle.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Tom Zanussi <zanussi@...cast.net>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [RFC PATCH 1/3] Unified trace buffer



On Thu, 25 Sep 2008, Steven Rostedt wrote:
> 
> The one thing that seemed to me most apparent from talking to people
> at LPC, is that they want a simple ring buffer API. If every tracer that
> uses this must come up with its own time keeping management, I don't think
> this will be used at all (except by those that are maintaining tracers
> now).

No, no.

The timestamp code is all in the ring buffer code. That was why I refused 
to have the layering without it.

And hell no, nobody should *ever* read the "tsc_delta" fields etc. Those 
are entirely internal to the buffering. If any user _ever_ reads or writes 
those on its own, it's a bug, plain and simple.

So when you read trace events, you should get the event data and the 
timestamp from the trace buffer routines. Nobody should ever even _see_ 
the internal trace buffer implementation!

			Linus
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