Re: [Discuss-gnuradio] GNURadio and CUDA reprised

[Michael Dickens]

I have a feeling -- from working with OpenCL for a while now (but, not in GNU 
Radio yet), watching profiling timing information (how long it takes to move 
data around, how long kernels take to get queued and executed) -- that what 
folks here have written seems mostly true: there is -significant- overhead so 
the number of computations must be quite high to make using a GPU "better" than 
just the CPU (if one is evaluating "better" just in terms of throughput, not 
taking into account that the GPU can be executed asynchronously w/r.t. the CPU 
& hence the combined "system" is generally actually faster overall than just 
using the CPU).  I think that if a GPU can be used, it will be most effective 
in things like filterbanks, or when searching for packets (via their unique 
sync sequence, so matched filtering), or very large FIR filters -- places where 
a LOT of computations and data must be processed and can be parallelized 
easily.  In my initial testing, doing something "simple" such as "c = a + b" is 
probably better left to vector units (e.g., use VOLK once it's fully 
functional) -- but, as I wrote above, if timing constraints can be met then the 
GPU can do work in parallel with the CPU & hence can increase system throughput 
somewhat even for such simple tasks.  More as I understand & program it; 
really, I'm still "in the beginning" of heading down this road ... If folks do 
make progress, I hope they post to this list for those of us interested in this 
topic. - MLD