RE: [Xen-devel] tsc_mode == 1 and hvm guests

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> However I can tell you that without the patch when vtsc == 1
> hvm_gtsc_need_scale returns 0 therefore scaling is never done.
> For this reason I cannot see how the tsc frequency would remain the
> same when vtsc == 1 and the underling hardware has a different tsc
> rate.
> The offset would be OK though.

I think when vtsc==1 (e.g. tsc_mode==1), no scaling is
done on HVM as the underlying machine is presented
to be a 1GHz machine (regardless of the true TSC rate
or whether migration had occurred or not).  PV also
presented only a 1GHz clock for awhile and I changed
it (with input from Jeremy as I recall) so that it
would be less confusing to end users who might be
confused by seeing Linux boot output claiming the
underlying machine "is only running at 1GHz!!".

There's a large number of different combinations to be
tested (and possibly broken) here.  I'd prefer to see
"I tested this feature on 4.0.0 and it doesn't work" before
putting a patch into the stable stream.  For xen-unstable
I have no problem with the patch of course.

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