On 10/17/2012 9:55 PM, Dave Mandelin wrote:
Following the recent discussion about PGO, I really wanted to understand what benefits
PGO gives Firefox on Windows, if any--I was skeptical. Rafael (IIRC) posted some Talos
numbers, but I didn't know how to interpret them. So I decided to try a few simple
experiments to try to falsify the hypothesis that "PGO has user-perceivable
benefits".
If you're interested in the benchmark side of things, it's fairly easy
to compare now that we build both PGO and non-PGO builds on a regular
basis. I'm having a little trouble getting graphserver to give me recent
data, but you can pick arbitrary tests that we run on Talos and graph
them side-by-side for the PGO and non-PGO cases. For example, here's Ts
and "Tp5 MozAfterPaint" for Windows 7 on both PGO and non-PGO builds
(the data ends in February for some reason):
http://graphs.mozilla.org/graph.html#tests=[[16,1,12],[115,1,12],[16,94,12],[115,94,12]]&sel=none&displayrange=365&datatype=running
You can see that there's a pretty solid 10-20% advantage to PGO in these
tests.
Here's Dromaeo (DOM) which displays a similar 20% advantage:
http://graphs.mozilla.org/graph.html#tests=[[73,94,12],[73,1,12]]&sel=none&displayrange=365&datatype=running
It's certainly hard to draw a conclusion about your hypothesis from just
benchmarks, but when almost all of our benchmarks display 10-20%
reductions on PGO builds it seems fair to say that that's likely to be
user-visible. We've spent hundreds of man-hours for perf gains far less
than that.
On a related note, Will Lachance has been tasked with getting our
Eideticker performance measurement framework working with Windows, so we
should be able to experimentally measure user-visible responsiveness in
the near future.
-Ted
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