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From: Nix <nix@esperi.org.uk>
To: Daniel Hazelton <dhazelton@enter.net>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	akpm@linuxfoundation.org, Jeff Dike <jdike@addtoit.com>,
	user-mode-linux-devel@lists.sourceforge.net,
	linux-kernel@vger.kernel.org
Subject: Re: [uml-devel] [PATCH 1/6] UML - Deal with host time going backwards
Date: Tue, 03 Jun 2008 20:52:18 +0100	[thread overview]
Message-ID: <878wxmfg99.fsf@hades.wkstn.nix> (raw)
In-Reply-To: <200806031543.56864.dhazelton@enter.net> (Daniel Hazelton's message of "Tue, 3 Jun 2008 15:43:56 -0400")

On 3 Jun 2008, Daniel Hazelton said:

> On Tuesday 03 June 2008 03:32:11 pm Andrew Morton wrote:
>> On Tue, 3 Jun 2008 15:02:35 -0400
>>
>> Jeff Dike <jdike@addtoit.com> wrote:
>> > Protection against the host's time going backwards - keep track of the
>> > time at the last tick and if it's greater than the current time, keep
>> > time stopped until the host catches up.
>>
>> Strange.  What would cause the host's time (or at least UML's perception
>> of it) to go backwards?
>
> A wild guess would be that the UML process is running "fast" at some point and 
> its expectation of the host's time is skewed forward because of that.

Quite so. Simply running ntp on the host (in slew-only mode, no less!) 
can cause this.

> Another possibility is that the hosts clock got reset between the times UML 
> has checked it and the correction was a negative one.

That too.

-- 
`If you are having a "ua luea luea le ua le" kind of day, I can only
 assume that you are doing no work due [to] incapacitating nausea caused 
 by numerous lazy demons.' --- Frossie

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  reply	other threads:[~2008-06-03 19:52 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-06-03 19:02 [uml-devel] [PATCH 1/6] UML - Deal with host time going backwards Jeff Dike
2008-06-03 19:32 ` Andrew Morton
2008-06-03 19:43   ` Daniel Hazelton
2008-06-03 19:52     ` Nix [this message]
2008-06-03 20:07       ` Andrew Morton
2008-06-03 20:37         ` Daniel Hazelton
2008-06-03 21:00         ` Jeff Dike
2008-06-04  1:50           ` Eric W. Biederman
2008-06-04  3:15             ` Jeff Dike
2008-06-04  5:12             ` Daniel Hazelton
2008-06-04 14:31           ` Jeremy Fitzhardinge
2008-06-04 19:37             ` Jeff Dike
2008-06-04 20:05               ` Jeremy Fitzhardinge
2008-06-05 15:30                 ` Jeff Dike
2008-06-05 18:14                   ` Nix
2008-06-05 19:47                     ` Jeff Dike
2008-06-05 21:41                       ` Nix
2008-06-05 18:19                   ` Nix
  -- strict thread matches above, loose matches on Subject: below --
2008-06-03 19:59 devzero

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