[igt-dev] [PATCH i-g-t 1/3] tests/perf_pmu: Tighten busy measurement

[Chris Wilson]

Quoting Chris Wilson (2018-02-01 17:08:09)
> Quoting Tvrtko Ursulin (2018-02-01 16:58:21)
> > 
> > I am just moving the two sample read-outs closer together in time. Two 
> > samples are measure of how long we slept, and measure of PMU busyness. 
> > There should be as little time as possible between the two readouts. 
> > Ending the spinner I don't see how it belongs in this sandwich, or 
> > anything else really.
> 
> Then we disagree on what we think we are measuring. The usleep should
> equal the busy value defined by the spin-batch.

How about if it was phrased:

	create spin-batch per-engine queued on a unsignal vgem
	open_group

	signal vgem // submit all queued spinners simultaneously (well, that's our goal)
	duration = measured_usleep
	end spinners

	busy = read_group

That's what I want to measure. The passage of time outside of the
spinner phase is then irrelevant, and the error inside is something that
we are trying to minimise as part of the driver overhead.
-Chris