ORC implementation of volk_32fc_magnitude_32f returns incorrect results on ARM about volk HOT 10 CLOSED

I did not observe the same issue on 64-bit Raspberry Pi OS, but I suspect it's because aarch64 support was only added do ORC in version 0.4.33, while Raspberry Pi OS has version 0.4.32.

from volk.

I suspect the current test suite would not catch this bug, since kernels are tested with random data. Perhaps some special-case values (0, 1, -1, std::numeric_limits<float>::max, std::numeric_limits<float>::min, std::numeric_limits<float>::epsilon, etc) should be included as well.

from volk.

That's a very difficult to solve issue. Basically, we'd need to work around the intended way ORC works. Or does this issue arise because of smth else? The comment in orctest.c implies this happens because of the specific implementation that is used in ORC on arm.

from volk.

The comment in orctest.c implies this happens because of the specific implementation that is used in ORC on arm.

That's correct. Only the ARM implementation is broken. I'd consider it a serious bug that sqrt(0) = NaN, but it seems ORC doesn't since they added an exception in their test suite: https://gitlab.freedesktop.org/gstreamer/orc/-/merge_requests/66

Perhaps a suitable workaround would be to disable the four affected VOLK kernels on ARM. That change could be reverted if ORC someday fixes their ARM sqrt implementation.

from volk.

Since the GQRX issues imply that the ORC implementation is slower than another, it doesn't hurt to disable these ORC kernels.

from volk.

On a Raspberry Pi 3B+ running 64-bit Raspberry Pi OS:

RUN_VOLK_TESTS: volk_32fc_magnitude_32f(131071,1987)
generic completed in 6106.05 ms
a_generic completed in 6125.19 ms
neon completed in 1808.37 ms
neon_fancy_sweet completed in 2292.84 ms
u_orc completed in 11231.1 ms
Best aligned arch: neon
Best unaligned arch: neon

RUN_VOLK_TESTS: volk_32f_sqrt_32f(131071,1987)
neon completed in 932.665 ms
generic completed in 12600.2 ms
u_orc completed in 13221.3 ms
Best aligned arch: neon
Best unaligned arch: neon

ORC is worse than generic in both cases, and much worse than neon.

from volk.

For volk_16ic_magnitude_16i and volk_16ic_magnitude_32f, the ORC kernels are already disabled on all platforms:

from volk.

damn, fancysweet isn't faster 👎

from volk.

Regarding the benchmarks #203 points out that ORC benchmarks include some one time overhead. We might need to test this.
On the other hand, the ORC kernel test runs 1987 iterations and takes more than 13s while the NEON kernel finishes in less than 1s. I really hope this one time ORC overhead is not included...

from volk.

This problem is now worse, because Debian 12 (and the latest Raspberry Pi OS) include ORC 0.4.33, which adds support for 64-bit ARM. As a result, these kernels are now broken on both 32-bit and 64-bit ARM.

from volk.