[PATCH 1/1] i915/query: Correlate engine and cpu timestamps with better accuracy

[Dixit, Ashutosh]

On Fri, 30 Apr 2021 19:19:59 -0700, Umesh Nerlige Ramappa wrote:
>
> On Fri, Apr 30, 2021 at 07:35:41PM -0500, Jason Ekstrand wrote:
> >   On April 30, 2021 18:00:58 "Dixit, Ashutosh" <ashutosh.dixit at intel.com>
> >   wrote:
> >
> >     On Fri, 30 Apr 2021 15:26:09 -0700, Umesh Nerlige Ramappa wrote:
> >
> >       Looks like the engine can be dropped since all timestamps are in sync.
> >       I
> >       just have one more question here. The timestamp itself is 36 bits.
> >        Should
> >       the uapi also report the timestamp width to the user OR should I just
> >       return the lower 32 bits of the timestamp?
> >
> >   Yeah, I think reporting the timestamp width is a good idea since we're
> >   reporting the period/frequency here.
>
> Actually, I forgot that we are handling the overflow before returning the
> cs_cycles to the user and overflow handling was the only reason I thought
> user should know the width. Would you stil recommend returning the width in
> the uapi?

The width is needed for userspace to figure out if overflow has occured
between two successive query calls. I don't think I see this happening in
the code.