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Re: [Xen-devel] [Patch] time resolution fix.

On 17 Mar 2006, at 14:39, Dong, Eddie wrote:

This patch fix HVM/VMX time resolution issue that cause IA32E complain
"loss tick" occationally and APIC time calibration issue.

not tested on SVM for slight common code change.

This patch looks scary. Can you give more info about the problem and how you solve it? It looks like you end up forcibly sync'ing the guest's TSC rate to the PIT rate? Would that even be necessary if the PIT emulation were moved into Xen, where it ought to be?

On a slightly unrelated note, I think TSC rate management will start to get exciting when we have HVM save/restore. What will happen if a guest is restored on a machine with quite different TSC rate to the machine it originally ran on? I was wondering whether the current TSC_OFFSET feature that VMX supports might be extended to allow control over TSC clock rate as well. For example, provide 'base' and 'scale' values and apply following when guest executes RDTSC:
 guest_tsc = (host_tsc - base) * scale + offset

How do you guys see this working?

 -- Keir

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