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

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Date:	Mon, 5 Mar 2012 22:16:54 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Dave Jones <davej@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	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 5, 2012 at 9:57 PM, Dave Jones <davej@...hat.com> wrote:
> 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.

I've reported this issue with regards to KVM before
(http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/85632) but
according to this thread it's not really KVM specific.

It's easily reproducible using Dave's trinity running inside a KVM guest.
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