The a and c vectors come from gr:fft objects' internal buffers. These are internally created with fftwf_malloc (lines 152/156 of gr-fft/lib/fft.cc). fftwf_malloc is obviously not generating buffers with proper alignment so you're seeing a 50% (per buffer) that this segfaults. I'll note that this is also only an issue with fftwf buffers when fftwf isn't built with AVX support (and therefore nothing in fftwf requires a 32-byte aligned buffer).
Andy Walls (thanks!) pointed out on IRC that we had a similar issue years ago with a QT sink. I have a branch that should fix this ( https://github.com/n-west/gnuradio/tree/fft-avx-alignment). I also suggest you look in to getting a version of fftwf built with AVX. I don't know if there's a good way to tell, but if I run readelf -a on my libfftw3.so I see some functions with avx in the name. Cheers, nw On Tue, Mar 8, 2016 at 1:31 PM, devin kelly <dwwke...@gmail.com> wrote: > OK, here's my C program: > > #include <stdio.h> > #include <stdlib.h> > #include <volk/volk.h> > #include <stdint.h> > > int main() { > > size_t alignment = volk_get_alignment(); > > uint8_t* ptr; > > ptr = (uint8_t*)volk_malloc(1000 * sizeof(uint8_t), alignment); > printf("alignment = %lu, ptr = %x, *ptr = %u\n", alignment, ptr, *ptr); > volk_free((void*)ptr); > ptr = NULL; > > > return 0; > } > > > Compile: > > $ gcc volk_test.c -o volk_test -lvolk -L/local_disk/gr_3.7.9_debug/lib > > It's output: > > $ ./volk_test > Using Volk machine: avx2_64_mmx_orc > alignment = 32, ptr = 151b040, *ptr = 00 > > Also, I've attached the output from the preprocessor, this command: > > $ /usr/bin/cc -DHAVE_AVX_CVTPI32_PS -DHAVE_CPUID_H -DHAVE_DLFCN_H > -DHAVE_FENV_H -DHAVE_POSIX_MEMALIGN -DHAVE_XGETBV -Wall -fvisibility=hidden > -g -I/local_disk/gr_3.7.9_src/volk/build_debug/include > -I/local_disk/gr_3.7.9_src/volk/include > -I/local_disk/gr_3.7.9_src/volk/kernels > -I/local_disk/gr_3.7.9_src/volk/build_debug/lib > -I/local_disk/gr_3.7.9_src/volk/lib -I/usr/include/orc-0.4 -E -fPIC -o > volk_malloc_preprocessed -c > /local_disk/gr_3.7.9_src/volk/lib/volk_malloc.c > > I just found the compiler step from from doing 'VERBOSE=1 make' then > changed the output and added -E. I attached volk_malloc_preprocessed as > well. > > It looks like this is my volk_malloc(): > > > void *volk_malloc(size_t size, size_t alignment) > { > void *ptr; > > > > > if (alignment == 1) > return malloc(size); > > int err = posix_memalign(&ptr, alignment, size); > if(err == 0) { > return ptr; > } > else { > fprintf(stderr, > "VOLK: Error allocating memory " > "(posix_memalign: error %d: %s)\n", err, strerror(err)); > return ((void *)0); > } > } > > > > Devin > > > > On Tue, Mar 8, 2016 at 11:37 AM, West, Nathan <n...@ostatemail.okstate.edu > > wrote: > >> >> On Tue, Mar 8, 2016 at 10:58 AM, devin kelly <dwwke...@gmail.com> wrote: >> >>> Calling 'info variables' (or args or locals) the last few frames didn't >>> give me any real info so I built a copy of GR/Volk with debug symbols. I >>> ran the FG again, this time from GDB, here's my back trace. In this >>> backtrace you can see the arguments passed in each call. I have an >>> i7-5600U CPU @ 2.60GHz, the volk_profile is appended at the bottom. >>> >> >> Excellent. Thanks for going through that extra step. It really helps. >> >> >>> >>> Here's are the links for the relevant code: >>> >>> >>> https://github.com/gnuradio/volk/blob/f0b722392950bf7ede7b32f5ff60019bce7a8592/kernels/volk/volk_32fc_x2_multiply_32fc.h#L232 >>> >>> https://github.com/gnuradio/gnuradio/blob/master/gr-filter/lib/fft_filter.cc#L323 >>> >>> https://github.com/gnuradio/gnuradio/blob/222e0003f9797a1b92d64855bd2b93f0d9099f93/gr-digital/lib/corr_est_cc_impl.cc#L214 >>> >>> Could the problem be that nitems is 257 and num_points is 512? Or >>> should nitems really be 256 and not 257? >>> >> >> I don't think so. I'm not familiar with the details of the fft_filter >> implementations, but usually these things will take in some history if they >> don't have enough points to operate on (in this case 512). >> >> The much more worrying thing is your vector addresses. >> >> >>> >>> Thanks, >>> Devin >>> >>> (gdb) bt >>> #0 0x00007fffdcaccb57 in volk_32fc_x2_multiply_32fc_a_avx2_fma >>> (__P=0x3b051b0) >>> at /usr/lib/gcc/x86_64-redhat-linux/4.8.5/include/avxintrin.h:835 >>> #1 0x00007fffdcaccb57 in volk_32fc_x2_multiply_32fc_a_avx2_fma >>> (cVector=0x3b1f770, aVector=0x3b051b0, bVector=0x3b240e0, num_points=512) >>> >> >> 0x3b1f770 % 32 = 16 (bad) >> 0x3b051b0 % 32 = 16 (bad) >> 0x3b240e0 % 32 = 0 (good) >> >> Unfortunately it looks like volk_get_alignment is returning the wrong >> thing or there's a bug in volk_malloc. Can you tell us what >> volk_get_alignment returns? The easiest thing is probably to write a simple >> C program that prints out the result (hmm, I should add that to >> volk-config-info). I'd also like to know which volk_malloc implementation >> you're using. Unfortunately I don't think we have an easy way to discover >> that (hmm, something else that should be added to volk-config-info). I >> think the best way might be to look at volk_malloc.c intermediate files >> after the preprocessor has done its work. >> >> If you want to move on while we figure this out then you can edit >> ~/.volk/volk_config and replace the avx2_fma with sse3 on the line that has >> this kernel name on it. >> >> >>> at >>> /local_disk/gr_3.7.9_src/volk/kernels/volk/volk_32fc_x2_multiply_32fc.h:242 >>> #2 0x00007fffdc945a75 in __volk_32fc_x2_multiply_32fc_a >>> (cVector=0x3b1f770, aVector=0x3b051b0, bVector=0x3b240e0, num_points=512) >>> at /local_disk/gr_3.7.9_src/volk/build_debug/lib/volk.c:7010 >>> #3 0x00007fffd3f8e360 in >>> gr::filter::kernel::fft_filter_ccc::filter(int, std::complex<float> const*, >>> std::complex<float>*) (this=0x3b02f40, nitems=nitems@entry=257, >>> input=input@entry=0x7fffc9cc7000, output=output@entry=0x3b36460) >>> at /local_disk/gr_3.7.9_src/gnuradio/gr-filter/lib/fft_filter.cc:323 >>> #4 0x00007fffd42910df in gr::digital::corr_est_cc_impl::work(int, >>> std::vector<void const*, std::allocator<void const*> >&, std::vector<void*, >>> std::allocator<void*> >&) (this=0x3b01560, noutput_items=257, >>> input_items=..., output_items=std::vector of length 1, capacity 1 = {...}) >>> at >>> /local_disk/gr_3.7.9_src/gnuradio/gr-digital/lib/corr_est_cc_impl.cc:237 >>> #5 0x00007fffdd064907 in gr::sync_block::general_work(int, >>> std::vector<int, std::allocator<int> >&, std::vector<void const*, >>> std::allocator<void const*> >&, std::vector<void*, std::allocator<void*> >>> >&) (this=0x3b015b8, noutput_items=<optimized out>, ninput_items=..., >>> input_items=..., output_items=...) at >>> /local_disk/gr_3.7.9_src/gnuradio/gnuradio-runtime/lib/sync_block.cc:66 >>> #6 0x00007fffdd02f70f in gr::block_executor::run_one_iteration() >>> (this=this@entry=0x7fff83ffedb0) >>> at >>> /local_disk/gr_3.7.9_src/gnuradio/gnuradio-runtime/lib/block_executor.cc:438 >>> #7 0x00007fffdd06da8a in >>> gr::tpb_thread_body::tpb_thread_body(boost::shared_ptr<gr::block>, int) >>> (this=0x7fff83ffedb0, block=..., max_noutput_items=<optimized out>) at >>> /local_disk/gr_3.7.9_src/gnuradio/gnuradio-runtime/lib/tpb_thread_body.cc:122 >>> #8 0x00007fffdd062761 in >>> boost::detail::function::void_function_obj_invoker0<gr::thread::thread_body_wrapper<gr::tpb_container>, >>> void>::invoke(boost::detail::function::function_buffer&) (this=0x3bc3ec0) >>> at >>> /local_disk/gr_3.7.9_src/gnuradio/gnuradio-runtime/lib/scheduler_tpb.cc:44 >>> #9 0x00007fffdd062761 in >>> boost::detail::function::void_function_obj_invoker0<gr::thread::thread_body_wrapper<gr::tpb_container>, >>> void>::invoke(boost::detail::function::function_buffer&) (this=0x3bc3ec0) >>> at >>> /local_disk/gr_3.7.9_src/gnuradio/gnuradio-runtime/include/gnuradio/thread/thread_body_wrapper.h:51 >>> #10 0x00007fffdd062761 in >>> boost::detail::function::void_function_obj_invoker0<gr::thread::thread_body_wrapper<gr::tpb_container>, >>> void>::invoke(boost::detail::function::function_buffer&) >>> (function_obj_ptr=...) at >>> /usr/include/boost/function/function_template.hpp:153 >>> #11 0x00007fffdd016cd0 in >>> boost::detail::thread_data<boost::function0<void> >::run() (this=<optimized >>> out>) >>> at /usr/include/boost/function/function_template.hpp:767 >>> #12 0x00007fffdd016cd0 in >>> boost::detail::thread_data<boost::function0<void> >::run() (this=<optimized >>> out>) >>> at /usr/include/boost/thread/detail/thread.hpp:117 >>> #13 0x00007fffdbe4f24a in thread_proxy () at >>> /lib64/libboost_thread-mt.so.1.53.0 >>> #14 0x00007ffff7800dc5 in start_thread () at /lib64/libpthread.so.0 >>> #15 0x00007ffff6e2528d in clone () at /lib64/libc.so.6 >>> >>> Here are the locals on the last few frames: >>> >>> (gdb) f 0 >>> #0 0x00007fffdcaccb57 in _mm256_load_ps (__P=0x3b051b0) at >>> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/include/avxintrin.h:835 >>> 835 return *(__m256 *)__P; >>> (gdb) info locals >>> No locals. >>> (gdb) f 1 >>> #1 volk_32fc_x2_multiply_32fc_a_avx2_fma (cVector=0x3b1f770, >>> aVector=0x3b051b0, bVector=0x3b240e0, num_points=512) >>> at >>> /local_disk/gr_3.7.9_src/volk/kernels/volk/volk_32fc_x2_multiply_32fc.h:242 >>> 242 const __m256 x = _mm256_load_ps((float*)a); // Load the ar + >>> ai, br + bi as ar,ai,br,bi >>> (gdb) info locals >>> y = {-4.87433296e+17, 4.59163468e-41, -3.92813517e+17, 4.59163468e-41, >>> 5.15677835e-43, 0, 5.26888223e-43, 0} >>> tmp2x = {6.389921e-43, 0, -512.314453, 4.59163468e-41, 1.26116862e-44, >>> 0, -4.87433296e+17, 4.59163468e-41} >>> x = {-512.314453, 4.59163468e-41, 0, 0, 2.76102662, -3.64918089, >>> -4.92134571, -1.06491208} >>> yl = {4.14784345e-43, 0, 1.26116862e-44, 0, -4.87442367e+17, >>> 4.59163468e-41, -4.87439343e+17, 4.59163468e-41} >>> yh = {-1674752, 4.59163468e-41, 0, 0, -1.50397414e-36, 4.59163468e-41, >>> -3.31452625e+17, 4.59163468e-41} >>> tmp2 = {6.72623263e-44, 1.2751816e-43, 2.24207754e-44, 0, >>> 7.17464814e-43, 0, -3.31440427e+17, 4.59163468e-41} >>> z = {0.794147611, 0, 0.263988227, 0, -0.380019426, 0, -0.953325868, 0} >>> number = 0 >>> quarterPoints = 128 >>> c = 0x3b1f770 >>> a = 0x3b051b0 >>> b = 0x3b240e0 >>> (gdb) f 2 >>> #2 0x00007fffdc945a75 in __volk_32fc_x2_multiply_32fc_a >>> (cVector=0x3b1f770, aVector=0x3b051b0, bVector=0x3b240e0, num_points=512) >>> at /local_disk/gr_3.7.9_src/volk/build_debug/lib/volk.c:7010 >>> 7010 volk_32fc_x2_multiply_32fc_a(cVector, aVector, bVector, >>> num_points); >>> (gdb) info locals >>> No locals. >>> (gdb) f 3 >>> #3 0x00007fffd3f8e360 in gr::filter::kernel::fft_filter_ccc::filter >>> (this=0x3b02f40, nitems=nitems@entry=257, >>> input=input@entry=0x7fffc9cc7000, output=output@entry=0x3b36460) at >>> /local_disk/gr_3.7.9_src/gnuradio/gr-filter/lib/fft_filter.cc:323 >>> 323 volk_32fc_x2_multiply_32fc_a(c, a, b, d_fftsize); >>> (gdb) info locals >>> a = <optimized out> >>> b = <optimized out> >>> c = <optimized out> >>> i = 0 >>> dec_ctr = 0 >>> j = <optimized out> >>> ninput_items = 257 >>> >>> My volk profile results: >>> >>> $ volk_profile -R 32fc_x2_multiply >>> Using Volk machine: avx2_64_mmx_orc >>> RUN_VOLK_TESTS: volk_32fc_x2_multiply_32fc(131071,1987) >>> u_avx2_fma completed in 220ms >>> u_avx completed in 220ms >>> u_sse3 completed in 240ms >>> generic completed in 2810ms >>> a_avx2_fma completed in 200ms >>> a_avx completed in 220ms >>> a_sse3 completed in 230ms >>> a_generic completed in 2810ms >>> u_orc completed in 280ms >>> Best aligned arch: a_avx2_fma >>> Best unaligned arch: u_avx2_fma >>> RUN_VOLK_TESTS: volk_32fc_x2_multiply_conjugate_32fc(131071,1987) >>> u_avx completed in 230ms >>> u_sse3 completed in 230ms >>> generic completed in 2790ms >>> a_avx completed in 220ms >>> a_sse3 completed in 230ms >>> a_generic completed in 2800ms >>> Best aligned arch: a_avx >>> Best unaligned arch: u_avx >>> Writing "/home/devin/.volk/volk_config"... >>> >>> >> Well I'm both jealous and happy that AVX2 is actually an improvement on >> newer processors. Also matches the folklore that these new technologies are >> usually not faster in the first silicon products that they come out in. >> > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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