Re: softtsc for PV guests

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 08/21/09 16:31, Dan Magenheimer wrote:
> Enabling CR4_TSD only traps ring>0 rdtscs.  Trapping guest kernel
> rdtsc's is ultimately necessary because the Linux kernel does NOT
> adequately handle all the possible changes in TSC characteristics
> that can occur if Xen moves an already booted guest from one
> physical machine to another (or even from one set of pcpus
> to another on certain physical machines).  I recognize this
> is very ugly, but it may be the only way to guarantee
> correctness 100% of the time.

PV guests already correct for that by using the data Xen provides; they
don't require Xen to do any correction or synthesis of tsc values.

> The system is definitely not dead, but dom0 is busy looping or
> something.  I can probably isolate the code, but the xen
> changes seem small enough that it's hard to believe they
> could cause this kind of problem.
>   

'0' on the Xen console will tell you where its spinning.  Oh, is it dom0
or domU?

    J