[Rock-dev] Usage of SSE* CPU features ...
Marc Hildebrandt
marc.hildebrandt at dfki.de
Mon Sep 5 17:33:10 CEST 2011
Last week I did some (not very exhaustive) tests with SSE on my i7 and
Dagon's i7 Mobile. In contrast to the measurements I did on the Core2Duo
architecture, I did not get any speedup with enabled SSE extensions on the
i7 CPUs. My Use-case was feature matching and general image processing
(rectify, histogram filter). After that I deactivated the SSE for the CUSLAM
packages. I would agree that we switch off all 'higher' SSE by default, and
come back to this issue when we find a package which really benefits from
SSE3+.
marc
-----Ursprüngliche Nachricht-----
Von: rock-dev-bounces at dfki.de [mailto:rock-dev-bounces at dfki.de] Im Auftrag
von Sylvain Joyeux
Gesendet: Montag, 5. September 2011 17:25
An: rock-dev at dfki.de
Betreff: [Rock-dev] Usage of SSE* CPU features ...
Some packages start to -- sometimes sneakily -- introduce dependence on
CPU features such as SSE*. Such packages are OpenCV and libelas
In libelas, this support is mandatory, so there's not much to do about it.
In OpenCV, it is experimental. The person that added opencv 2.3 to rock
turned these features ON by default.
My question:
* is opencv using an autodetection feature ? I.e. does it turn them
off at runtime if the CPU does not support them, or will the user get a
"wrong instruction" error ?
* in the latter case, what should be the default ? I would go for "do
not enable SSE >= 4 by default" and explain how to enable it to users on
the wiki. For OpenCV, it would be reenabled by adding the following code
snippet in autoproj/overrides.rb
setup_package("external/opencv") do |pkg|
pkg.define("ENABLE_SSE41","ON")
pkg.define("ENABLE_SSE42","ON")
pkg.define("ENABLE_SSSE3","ON")
end
For the time being, I disabled SSE >= 4 in the rock package set (that
seems to be the safest until we resolve the question).
--
Sylvain Joyeux
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