On Sat, 2008-11-15 at 10:30 -0500, Marcus D. Leech wrote: > What is the current status of GPU support in Gnu Radio? In particular, > a GPUed FFT implementation would be peachy keen. > I have been working on this for quite some time now. I did a glsl implementation a few years back but it didn't perform that well and had some severe limitations.
So I started over this year and have reimplemented major part of GnuRadio using CUDA. It is a one to one implementation. (every gr_something block is replaced with a cuda_something block) My work-in-progress code is at: http://gnuradio.org/trac/browser/gnuradio/branches/developers/nldudok1/gpgpu-wip Make sure you read http://gnuradio.org/trac/browser/gnuradio/branches/developers/nldudok1/gpgpu-wip/README.cuda Caleb Phillips made a wiki about my code, you can find it at: http://www.smallwhitecube.com/php/dokuwiki/doku.php?id=howto:gnuradio-with-cuda The majority of the gnuradio-core code is a unmodified gnuradio checkout of a few moths back. There are some important changes in gnuradio_core/src/lib/runtime to support CUDA device memory as an emulated circular buffer. I also implemented a gr.check_compare block which expects two input streams and checks if they are outputting the same data. I use this to check if my cuda blocks do exactly the same as the gr blocks. All the rest of the CUDA code is in gr_cuda. gr_cuda has to be configured and build seperately. gr_cuda is where the cuda reimplementations of some gnuradio blocks are. Then there are also a few new blocks cuda_to_host and host_to_cuda which copy memory from and to the GPU device memory. All python scripts to test and use the code are in /testbed. The code in testbed is changing on a day-by-day basis. There are several issues to be well aware of when doing SDR on a GPU. -overhead -call overhead -copying data from and to the GPU You need to do a lot of work on the GPU in one call to have any benefit. -circular buffers -GPU memory cant't be mmapped into a circular buffer -solution 1: use copying to emulate a circular buffer -solution 2: keep track of all the processing and make your own intelligent scheduler which does not need a circular buffer. -threads: with CUDA you can't access GPU device memory from different host-threads. So make sure you create use and destroy all device memory from the same thread. (The standard GnuRadio scheduler does not do it like this) -debugging: Debugging is hard and works quite different from normal debugging. -parallel: The GPU is good in doing calculations in parallel which are not dependant on each other. For this reason a FIR will perform well, while an IIR will perform bad. An IIR can only use one processing block of the GPU, in stead of 128. It can still be benificial to do the IIR on the GPU when all your other blocks are running on the GPU because you don't have to copy all samples to the CPU, do the IIR on the CPU and copy everything back to the GPU. All that said. I do have a complete WFM receiver which is running completely on the GPU. (using FIR and/or FFT filters, quadrature_demod, fm-deemph) The FFT filters use the cuda provided FFT. It shouldn't be too hard to use the FFT for other things (just look at the code of gr_cuda/src/lib/cuda_fft_*) At the moment the complete wfm receiver is not running faster then on the CPU with my 9600GT card, mainly because of the call overhead. (too little work items done per call) And the extra copying done to emulate circular buffers. I can increase the amount of work done per call by using output_multiple. But with the current scheduling code the flow-graph can hang. This needs work. So the performance will change in the future. First I want to make sure everything is working as expected. If I benchmark a single block with a big output_multiple then I do see performance increases. Greetings, Martin _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio