On Mon, Nov 12, 2012 at 4:55 AM, "Martin Lülf" <m...@mluelf.de> wrote: >> On Fri, Nov 9, 2012 at 11:47 AM, "Martin Lülf" <m...@mluelf.de> wrote: >>> Hi list, >>> >>> I am trying to speed up my own gnuradio block using volk. Besides using >>> volk on gnuradios input and output buffers I also want do use it with my >>> own arrays. I found this Thread in the mailing list archive >>> http://lists.gnu.org/archive/html/discuss-gnuradio/2012-09/msg00055.html >>> which shows how to allocate aligned memory and I also tried using >>> posix_memalign directly as well (see the code below). Both end in the >>> same >>> result: If I run my block with the aligned volk_32fc_x2_multiply_32fc_a >>> kernel my application crashes with a Segmentation fault. I checked with >>> a >>> debugger and it is the volk call at which the segfault happens. I get no >>> segfaults for the unaligned version volk_32fc_x2_multiply_32fc_u. My >>> flowgraph is created with grc and just contains of >>> signal_source->my_block->null_source >>> >>> Running volk_profile, sse3 is selected for both kernels (and the aligned >>> version does not segfault here), so there has to be an issue with my >>> code. >>> >>> I am working on an Intel Xeon X5690 CPU with an 3.2.0-32-generic >>> #51-Ubuntu SMP Wed Sep 26 21:33:09 UTC 2012 x86_64 x86_64 x86_64 >>> GNU/Linux >>> and gnuradio-3.6.0 >>> >>> I know that there is a newer version of gnuradio available but before >>> turning my whole system upside-down I'd like to know if there is >>> anything >>> wrong with the minimal code example below. >>> >>> Any help is appreciated. >>> Yours >>> Martin >> >> Martin, >> >> The problem is in your constructor. You have not told the block to >> work with your alignment. In blocks that use VOLK, we have this in the >> constructor: >> >> const int alignment_multiple = >> volk_get_alignment() / sizeof(gr_complex); >> set_alignment(std::max(1, alignment_multiple)); >> >> We divide the alignment by sizeof(output type) specifically. We should >> be able to hide this in the future, but there's some uncertainty as to >> whether the output type is always the right answer if there are >> multiple types defined, so we do the right thing for each block. >> >> Also, a general note on using fftwf_malloc that I found out the hard >> way. If you have an AVX processor and want to use AVX kernels, FFTW >> needs to be build using --enable-avx. I've had to build FFTW by hand >> on my AVX processors where I want to use VOLK. >> >> Tom >> >> > > Hi Tom, > > thank you very much for your help. Adding the few lines to my constructor > solved the segfault problem. Now I am trying to understand what I did :) > > I assumed with calling set_alignment I tell the scheduler on which bounds > he should try to align, which will result in more aligned arrays being > passed to work. However even without telling the scheduler which alignment > I would like to have is_unaligned() should never return false, when the my > input or output arrays are unaligned and thus in the worst case the > unaligned kernel is called, although the arrays are indeed aligned, but > not the other way around. What am I missing here? > > Yours > Martin
set_alignment sets up the alignment boundaries, but it also initializes the variables for when the item streams are aligned; without the initialization, the scheduler has no idea how to keep track of anything. You can use the volk_is_aligned, which will actually test the pointer's alignment and tell you if it's aligned or not. Tom _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
