Re: [Xen-devel] [PATCH RFC] x86/lapic: remove the PIT usage to calibrate the lapic timer

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

Roger Pau Monne <roger.pau@xxxxxxxxxx> writes:

> And instead use NOW which is based on the TSC. This was already used
> when running in shim mode, since there's likely no PIT in that
> environment.
>
> Remove printing the CPU frequency, since it's already printed earlier
> at boot, and getting the CPU frequency against the TSC without any
> external reference timer is pointless.
>
> The motivation behind this change is to allow Xen to boot on HyperV
> gen2 instances, which lack a PIT.

When on Hyper-V, LAPIC frequency can easily be queried from
HV_X64_MSR_APIC_FREQUENCY (and that's what Linux does nowdays). This, of
course, only if Hyper-V provides the interface but it always does.

-- 
  Vitaly

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