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SubjectRe: [patch 00/11] x86/vdso: Cleanups, simmplifications and CLOCK_TAI support
Marcelo Tosatti <> writes:

> On Wed, Oct 03, 2018 at 11:22:58AM +0200, Vitaly Kuznetsov wrote:
>> There is a very long history of different (hardware) issues Marcelo was
>> fighting with and the current code is the survived Frankenstein.
> Right, the code has to handle different TSC modes.
>> E.g. it
>> is very, very unclear what "catchup", "always catchup" and
>> masterclock-less mode in general are and if we still need them.
> Catchup means handling exposed (to guest) TSC frequency smaller than
> HW TSC frequency.
> That is "frankenstein" code, could be removed.
>> That said I'm all for simplification. I'm not sure if we still need to
>> care about buggy hardware though.
> What simplification is that again?

I was hoping to hear this from you :-) If I am to suggest how we can
move forward I'd propose:
- Check if pure TSC can be used on SkyLake+ systems (where TSC scaling
is supported).
- Check if non-masterclock mode is still needed. E.g. HyperV's TSC page
clocksource is a single page for the whole VM, not a per-cpu thing. Can
we think that all the buggy hardware is already gone?


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