Re: tsc_mode == 1 and hvm guests

[Keir Fraser <keir.fraser@eu.citrix.com>]

Should Cc Dan on this, as he's the original implementer.

 K.

On 06/05/2010 12:41, "Stefano Stabellini" <Stefano.Stabellini@eu.citrix.com>
wrote:

> Hi all,
> going through the vtsc code in xen I realized that vtsc_offset and, more
> importantly, vtsc_to_ns/ns_to_vtsc are never used for hvm guests.
> That means that if tsc_mode == 1 the rdtsc values returned to pv guests
> and the ones returns to hvm guests are fundamentally different because
> in the first case they are scaled by the guest tsc frequency and in the
> second case they are not.
> The fact that noone at the moment is calling tsc_set_info with gtsc_khz
> != 0 doesn't help spotting this problem.
> 
> Is there a reason for this or is it just a bug?
> 
> Also there are two gtsc_khz AFAICT: d->arch.tsc_khz and
> d->arch.hvm_domain.gtsc_khz, why hvm guests have their own separate
> record of the guest tsc frequency, when they never actually change it?
> 
> BTW I noticed these problems because they prevent the pvclock algorithm
> from working correctly in a PV on HVM linux guest.
> 
> Thanks,
> 
> Stefano
> 
> 
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