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

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Date:	Thu, 25 Sep 2008 14:02:53 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...e.hu>, Martin Bligh <mbligh@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Martin Bligh <mbligh@...igh.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, 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

Linus Torvalds wrote:
> As for C2/C3 - that's just an argument for *not* doing anything at trace 
> time. What do you think happens when you try to trace through those 
> things? You're much better off trying to sort out the problems later, when 
> you don't hold critical locks and are possibly deep down in some buggy 
> ACPI code, and you're trying to trace it exactly _because_ it is buggy.
>   

That suggests that frequency changes should be recorded at a lower layer
as well, along with full timestamps and deltas, so that a log parser can
correctly generate the timestamps without having to parse higher-level
trace records.  Maybe the simplest thing to do is make the full
timestamp records also include frequency and offset information (to deal
with discontinuities caused by things like a vcpu switching between
physical cpus with unsynced tscs).

    J
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