From owner-cvs-all  Wed Jul 28 13:52:26 1999
Delivered-To: cvs-all@freebsd.org
Received: from dingo.cdrom.com (dingo.cdrom.com [204.216.28.145])
	by hub.freebsd.org (Postfix) with ESMTP
	id 657EC15563; Wed, 28 Jul 1999 13:52:17 -0700 (PDT)
	(envelope-from mike@dingo.cdrom.com)
Received: from dingo.cdrom.com (localhost.cdrom.com [127.0.0.1])
	by dingo.cdrom.com (8.9.3/8.8.8) with ESMTP id NAA00544;
	Wed, 28 Jul 1999 13:46:32 -0700 (PDT)
	(envelope-from mike@dingo.cdrom.com)
Message-Id: <199907282046.NAA00544@dingo.cdrom.com>
X-Mailer: exmh version 2.0.2 2/24/98
To: Poul-Henning Kamp <phk@critter.freebsd.dk>
Cc: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sys/i386/apm apm.c apm_setup.s apm_setup.h src/sys/i386/isa clock.c 
In-reply-to: Your message of "Wed, 28 Jul 1999 22:32:16 +0200."
             <65418.933193936@critter.freebsd.dk> 
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Date: Wed, 28 Jul 1999 13:46:32 -0700
From: Mike Smith <mike@smith.net.au>
Sender: owner-cvs-all@FreeBSD.ORG
Precedence: bulk

> In message <199907282022.NAA25414@freefall.freebsd.org>, Mike Smith writes:
> 
> >  In reality, even this isn't good enough; regardless of whether we support
> >  APM or not, the system may well futz with the CPU's clock speed and throw
> >  the TSC off.  We need to stop using it for timekeeping except under
> >  controlled circumstances.
> 
> I'd rather we stop using if it looks manipulated.  I have looked at various
> ways to improve the calibration of the TSC by spending longer time doing it,
> this is however not enough to detect a manipulated TSC because the timeouts
> in the bios may be half and whole hours.

Basically, the BIOS' behaviour has to be considered to be 
nondeterministic.

> It can probably be detected by examining "elapsed wall-clock time" in 
> hardclock, and comparing to hz with some margin for jitter.

Go for it...

-- 
\\  The mind's the standard       \\  Mike Smith
\\  of the man.                   \\  msmith@freebsd.org
\\    -- Joseph Merrick           \\  msmith@cdrom.com




To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe cvs-all" in the body of the message