RE: [Xen-ia64-devel] SMP guest and itc

[Alex Williamson <alex.williamson@xxxxxx>]

On Tue, 2006-02-14 at 18:10 +0800, Dong, Eddie wrote:
> Alex:
>       Can't exposing an formula cooperatively between domain &
> hypervisor solve the prpblem?
>       E.g:   guest_ITC=host_ITC * fact + offset;    If the host ITC is
> accurate enough.
>       Or guest_ITC = host_high_precise_timer_count * fat + offset; if
> the hyprevisor want to use other platform high precise timer like HPET.
>       Implementing those one in xenlinux is quit easy IMO.

Hi Eddie,

   I guess I'm not sure what you mean by exposing the formula
cooperatively.  Could you explain?  I'm thinking along the lines of
trapping access to the ITC and emulating, but you mention in a separate
email that a trap isn't required.

>       One more thing for time virtualization for us is to implement
> other timer resource virtualization like ACPI timer, HPET that may be
> used optionally.

   Definitely, this is where I was thinking a paravirtualized time
interpolator might also work well.  The xen backend of the code could
could use the HPET or ITC depending on what's available on the platform.
Once we do that, I'm not sure how valuable the fully virtualized ITC
would be.  I don't think that one necessarily excludes the other, they
may be complimentary together.  Thanks,

        Alex



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