Re: [Xen-devel] CR4.TSD in guest kernel vs userland

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 22.09.09 08:34 >>>
>It's only likely to be reasonable for PV 64-bit guests, which transition via
>the hypervisor already for guest-kernel <-> guest-app transitions (i.e.,
>those transition times suck already).

But still, I don't think adding a serializing instruction that likely (I don't
know of officially available numbers) takes hundreds of clocks is a good
thing to do.

Jan

>On 21/09/2009 23:49, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:
>> I was fretting about the overhead of emulating TSC in
>> guest kernels.  Is it possible (and relatively inexpensive)
>> to change CR4.TSD on every transition between guest
>> kernel and userland?  I suspect not, but thought
>> I'd check.  If so, what about HVM vs PV and 32-bit
>> vs 64-bit guest.



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