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

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@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.