On Thu, 28 Jun 2018, Peter Zijlstra wrote:
> On Thu, Jun 28, 2018 at 12:43:59PM +0200, Thomas Gleixner wrote:
> > init_hypervisor_platform()
> > vmware:
> > Retrieves frequency and store it for the
> > calibration function
> >
> > khz = vmware_get_khz_magic()
> > vmware_tsc_khz = khz
> > calibrate_cpu = vmware_get_tsc_khz
> > calibrate_tsc = vmware_get_tsc_khz
> > preset_lpj(khz)
> >
> > hyperv:
> > if special hyperv MSRs are available:
> >
> > calibrate_cpu = hv_get_tsc_khz
> > calibrate_tsc = hv_get_tsc_khz
> >
> > MSR is readable already in this function
> >
> > jailhouse:
> >
> > Frequency is available in this function and store
> > in a variable for the calibration function
> >
> > calibrate_cpu = jailhouse_get_tsc
> > calibrate_tsc = jailhouse_get_tsc
> >
> > ...
> >
> > kvmclock_init()
> >
> > if (magic_conditions)
> > calibrate_tsc = kvm_get_tsc_khz
> > calibrate_cpu = kvm_get_tsc_khz
> >
> > kvm_get_preset_lpj()
> > khz = kvm_get_tsc_khz()
> > preset_lpj(khz);
>
> Note that all these which get TSC values from a HV _should_ set
> X86_FEATURE_TSC_KNOWN_FREQ to avoid the late recalibrate.
True.
> Calibrating against a virtual PIT/HPET/PMTIMER is utterly pointless.
It kinda works :)
> > The generic initilizaiton does everything twice, which makes no sense,
> > except for the unlikely case were no fast functions are available and the
> > quick PIT calibration fails (PMTIMER/HPET) are not available in early
> > calibration. HPET
>
> Incomplete; but I suspect you want to talk about how we can make HPET
> available early by putting it in a fixmap.
As I figured out now that's only part of the picture. We also need to do
that past x86_dtb_init() because early_quirks() and the early acpi/sfi/dtb
stuff needs to be completed before it makes sense to access hpet. But at
that point we also have the PMTIMER info.
> And only if we fail, do we at a later stage try again using PMTIMER.
>
> Currently it all works by accident, since !hpet and acpi_pm_read_early()
> returns 0, but really we should not be running the fallback crap at all
> that early.
Right.
Thanks,
tglx
