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RE: [Xen-devel] softtsc for PV guests

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: RE: [Xen-devel] softtsc for PV guests
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Mon, 24 Aug 2009 10:58:00 -0700 (PDT)
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> > I just got a big clue... the next line of console output in a
> > successful boot AFTER the EXT3-fs mounting message is from
> > the Real Time Clock Driver.  That sounds like something that
> > might be affected by rdtsc changes.
> >   
> Ah, yes.  It may be doing some calibration thing which never converges
> with a slow rdtsc.  But that would be pretty obvious from 
> looking at the
> eip/rip.

No, the clue led me astray.  The code in RTC was never reached.
The eip pointed me to the probable answer:  I think this is the
first time a userland rdtsc is executed, Xen is "reflecting"
the GPF to Linux, Linux doesn't really know what to do with the
GPF and would like to deliver a signal to userland but theres
no signal registered for it, so nobody ever updates the IP and
an infinite loop results.  So more work needed on my part to
fix this.

More on the general topic later.


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