Re: [Xen-devel] [PATCH v2 2/5] x86: Begin to remove TSC mode PVRDTSCP

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.11.18 at 15:36, <andrew.cooper3@xxxxxxxxxx> wrote:
> For more historical context, see
>   c/s c17b36d5dc792cfdf59b6de0213b168bec0af8e8
>   c/s 04656384a1b9714e43db850c51431008e23450d8
> 
> PVRDTSCP was an attempt to provide Xen-aware userspace with a stable monotonic
> clock, and enough information for said userspace to cope with frequency
> changes across migrate.  However, the PVRDTSCP infrastructure has resulted in
> very tangled code, and non-architectural behaviour even in non-PVRDTSCP cases.
> 
> Seeing as the functionality has been replaced entirely by improvements in PV
> clocks (including being plumbed into the VDSO nowadays), or alternatively by
> hardware TSC scaling features, and no-one is aware of any users of this mode,
> take the opportunity to remove it.
> 
> For now, drop TSC_MODE_PVRDTSCP from tsc_{get,set}_info().  This will catch
> and cleanly reject attempts to migrate in a VM configured to use PVRDTSCP,
> rather than letting it run and have the wrong timing mode.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>



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