[cairo] update on cairo-gl performance

[Chris Wilson]

Excerpts from Kai-Uwe Behrmann's message of Thu Oct 22 06:55:59 +0100 2009:
> Am 20.10.09, 15:56 -0700 schrieb Eric Anholt:
> > Finally, the numbers:
> >
> > [ # ]  backend                         test   min(s) median(s) stddev. count
> 
> Does the numbers read like minutes in opposite to frames per second?

Indeed. The measurement is the duration of the test run. Each test
represents a trace of an application doing a fixed quantity of real
work, which aims to give us a sense of overall system improvement for
each change.

As has been pointed out, they do not represent ideal cases, but
snapshots of real world usage. If an application makes a substantial
improvement to its rendering engine (like poppler has recently done), we
will drop the old trace and replace it, as we do not wish to continue
optimising for obsolete behaviour.

Similarly, it would be useful for application level benchmarks to put
the gfx system in perspective. There are few applications that are
particularly sensitive to gfx throughput (as being measured here) - but
some may be very sensitive to any latency between input and the (initial)
result being visible. And then there are applications where consistent
throughput is paramount, and even tiny stutters are highly visible - cases
where both high throughput and low, consistent, latency is required.

cairo-perf-trace has been a tremendous step forward for us to be able to
make quantifiable changes to the gfx stack. I hope that we will in the
future have similar benchmarks to drive further improvements across the
whole desktop (and shift the focus away from throughput being paramount).
-ickle
-- 
Chris Wilson, Intel Open Source Technology Centre