[PATCH] vulkan: Add VK_EXT_calibrated_timestamps extension (radv and anv) [v4]

[Keith Packard]

Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl> writes:

> You can make the monotonic case the same as the raw case if you make
> sure to always sample the CPU first by e.g. splitting the loops into
> two and doing CPU in the first and GPU in the second. That way you
> make the case above impossible.

Right, I had thought of that, and it probably solves the problem for
us. If more time domains are added, things become 'more complicated'
though.

> That said "start of the interval of the tick" is kinda arbitrary and
> you could pick random other points on that interval, so depending on
> what requirements you put on it (i.e. can the chosen position be
> different per call, consistent but implicit or explicitly picked which
> might be leaked through the interface) the max deviation changes. So
> depending on interpretation this thing can be very moot ...

It doesn't really matter what phase you use; the timer increments
periodically, and what really matters is the time when that happens
relative to other clocks changing.

-- 
-keith
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