linux-kernel - Re: WARNING: Adjusting tsc more then 11%

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Message-ID: <20120305195758.GA25498@redhat.com>
Date:	Mon, 5 Mar 2012 14:57:58 -0500
From:	Dave Jones <davej@...hat.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Fedora Kernel Team <kernel-team@...oraproject.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: WARNING: Adjusting tsc more then 11%

On Mon, Mar 05, 2012 at 11:50:10AM -0800, John Stultz wrote:

 > >  > > The reports seem to have started around 3.3-rc4.
 > > thinking about this some more, while the reports starts around rc4, this
 > > may have been caused by something prior to that, as anyone moving from
 > > Fedora 16 or earlier to F17 alpha would have jumped quite a kernel version or two.
 > 
 > Was F16 3.1 based? The warning was added in 3.2, so if you skipped it,
 > it may not be new behavior then.

initially 3.1 based. We recently pushed out a rebase to 3.2.
This bug hasn't shown up there (yet?)

 > Ok. Well, just to level set: the warning is informative, and points to
 > unexpected, but not necessarily unsafe behavior.
 >
 > In fact, the risk (where mult is adjusted to be large enough to cause an
 > overflow) we're warning about have been present 2.6.36 or even possibly
 > before. The change in 3.2 which added the warning also added a more
 > conservative mult calculation, so we're less likely to get overflow
 > prone large mult values.
 > 
 > So it would be great to get further feedback from folks who are seeing
 > this warning, so we can really hammer this out, but I don't want the
 > warning spooking anyone into thinking things are terribly broken.
 
One of the reports was from someone using vbox. I'm now wondering if
the other users are using some other flavour of virt. I'll ask.
 
	Dave

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