15 Apr
2008
15 Apr
'08
4:12 p.m.
On Tue, 2008-04-15 at 19:45 +0200, Christian Schoenebeck wrote:
Yeah, I'm respawning this topic ...
because I was curious how the GCC vector extension situation changed meanwhile
and wrote a small benchmark for mixing signals with and without gain. You can
find it here:
http://download.linuxsampler.org/dev/mixdown.tar.gz
I compared a pure C++ implementation vs. the hand crafted SSE assembly code
(by Sampo Savolainen, Ardour) and of course an implementation utilizing GCC's
vector extensions. On my very weak, but environment friendly ;-) VIA box the
GCC vector implementation outperforms the other two solutions (using GCC
4.2.3 BTW):
Benchmarking mixdown (no coeff):
pure C++ : 670 ms
ASM SSE : 200 ms
GCC vector extensions : 180 ms
Benchmarking mixdown (WITH coeff):
pure C++ : 890 ms
ASM SSE : 300 ms
GCC vector extensions : 230 ms
Great stuff, very interesting. It seems it's finally getting easier to
vectorize functions. Too bad the code is awfully slow for non-sse
compiles. That still leaves the responsibility of choosing the fastest
algorithms per architecture at runtime to the application developers.
What about gcc 4.3.0 performance? I seem to recall that 4.3 should have
even better vectorization support.
I have to test whether I could squeeze a few more cycles out of
compute_peak(). That algorithm is the sole reason I started writing SSE
for ardour. The function uses a huge amount of computing time without
optimization.
Sampo