[maemo-developers] Performance of floating point instructions

[From: Alberto Mardegan]

Siarhei Siamashka wrote:
>> The output (application compiled with -O0):
> 
> Using an optimized build (-O2 or -O3) may sometimes change the overall picture
> quite dramatically. It makes almost no sense benchmarking -O0 code, because in
> this case all the local variables are kept in memory and are read/written
> before/after each operation. It's substantially different from normal code.

Right. Just to complete the picture, here's the same data with -O2:

float (fast mode enabled):
map_path_calculate_distances: 40 ms for 8250 points
map_path_calculate_distances: 2 ms for 430 points

double (fast mode enabled):
map_path_calculate_distances: 93 ms for 8250 points
map_path_calculate_distances: 4 ms for 430 points

(I'm not posting the same data with fast mode disabled, as it cannot be 
worse than the -O0 case, which is anyway not too far from these values)
The relative preformance seems to be about the same. But then of course, 
it might not be because of the FPU, but of the data transfers.

Ciao,
   Alberto

-- 
http://www.mardy.it <- geek in un lingua international!