Re: [Xen-devel] [PATCH] [HVM] Fix virtual apic irq distribution

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 27 Jun 2006, at 12:39, Li, Xin B wrote:

> But on our VM, we will have to synchronize TSC from time to time, so 
> PIT
> irq handler on different vcpu may see big TSC diff and complain about
> the unreliable TSC, then maybe it will try to do TSC sync, which make
> guest time keeping complex and unreliable.
How out-of-sync do TSCs of different VCPUs get?

I'd like to see a non-optimised TSC mode in which RDTSC always vmexits 
and we implement constant-rate always-sync'ed TSC in Xen. It'd be good 
to see if we could at least get that time mode working properly, and 
we'll need it anyway for save/restore/migration between machines with 
(even only slightly) different clock speeds or the guest will get very 
confused.
 -- Keir


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