On 1/31/2013 10:51 AM, Ehsan Akhgari wrote:
On 2013-01-31 11:43 AM, Kyle Huey wrote:
On Wed, Jan 30, 2013 at 8:03 PM, Ehsan Akhgari <ehsan.akhg...@gmail.com
<mailto:ehsan.akhg...@gmail.com>> wrote:
We then tried to get a sense of how much of a win the PGO
optimizations are. Thanks to a series of measurements by dmandelin,
we know that disabling PGO/LTCG will result in a regression of about
10-20% on benchmarks which examine DOM and layout performance such
as Dromaeo and guimark2 (and 40% in one case), but no significant
regressions in the startup time, and gmail interactions. Thanks to
a series of telemetry measurements performed by Vladan on a Nightly
build we did last week which had PGO/LTCG disabled, there are no
telemetry probes which show a significant regression on builds
without PGO/LTCG. Vladan is going to try to get this data out of a
Tp5 run tomorrow as well, but we don't have any evidence to believe
that the results of that experiments will be any different.
Isn't PGO worth something like 15% on Ts?
That was what I thought, but local measurements performed by dmandelin
proved otherwise.
For what it's worth, reading
<https://bugzilla.mozilla.org/show_bug.cgi?id=833890>, I do not get the
impression that dmandelin "proved" otherwise. His startup tests have
very low statistical confidence (n=2, n=3), and someone who disclaims
his own findings. It may be evidence that PGO is not a Ts win, but it is
weak evidence at best. Our Talos results may be measuring imperfect
things, but we have enough datapoints that we can draw statistical
conclusions from them confidently. If you want to argue to me that
they're wrong, you're going to have produce more compelling evidence.
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