Re: [Xen-devel] Re: Ping: Timer ISR backwards notices

[Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>]

On Mon, Jan 10, 2005 at 09:42:25AM -0800, Jared Rhine wrote:
> > > I'm getting a lot of "Timer ISR: Time went backwards" printk's,
> 
> I get the problems also under qemu and bochs (as well as the previously
> reported vmware), but I haven't compared to a real machine yet.

I've seen these messages when running under vmware.
The most likely cause for this is that the delay between when xen
updates the domain's time value and when the domain gets to read it
can become arbitrarily large if the emulator gets descheduled by
the host operating system or when the emulator has to schedule
between multiple emulated/virtual machines.  In that case the
value read from the tsc can have advanced sufficiently so that
the 32 bit we use to interpolate exact time has wrapped.

    christian



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