linux-kernel - Re: Unified tracing buffer

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Message-ID: <33307c790809221712x4fbd9781u958c98d4585e92a9@mail.gmail.com>
Date:	Mon, 22 Sep 2008 17:12:51 -0700
From:	"Martin Bligh" <mbligh@...gle.com>
To:	"Masami Hiramatsu" <mhiramat@...hat.com>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Mathieu Desnoyers" <compudj@...stal.dyndns.org>,
	"Steven Rostedt" <rostedt@...dmis.org>, darren@...art.com,
	"Frank Ch. Eigler" <fche@...hat.com>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: Re: Unified tracing buffer

>> I think we came up with a way to approximate this, using a callback every
>> ms or so as the higher order bits, and a sequential counter in the lower
>> order for those broken platforms.
>
> Sure, that will work.

OK, that'd fix 99% of it, even if we only get time within 1ms or so (but still
good ordering).

>> But perhaps it would be better if we started with a discussion of which
>> platforms can't do global timestamps, and why not? I know some of them
>> are fixable, but perhaps not all.
>
> For example, my laptop (this machine/Core2Duo) doesn't return correct TSC. :-(

Can you define incorrect for me (in this case)?

We had similar problems with some AMD platforms that we can fix by syncing
the TSCs on exit_idle, etc.
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