> -----Original Message----- > From: Nathan Bossart <nathandboss...@gmail.com> > Sent: Thursday, March 28, 2024 2:39 PM > To: Amonson, Paul D <paul.d.amon...@intel.com> > > * The latest patch set from Paul Amonson appeared to support MSVC in the > meson build, but not the autoconf one. I don't have much expertise here, > so the v14 patch doesn't have any autoconf/meson support for MSVC, which > I thought might be okay for now. IIUC we assume that 64-bit/MSVC builds > can always compile the x86_64 popcount code, but I don't know whether > that's safe for AVX512.
I also do not know how to integrate MSVC+Autoconf, the CI uses MSVC+Meson+Ninja so I stuck with that. > * I think we need to verify there isn't a huge performance regression for > smaller arrays. IIUC those will still require an AVX512 instruction or > two as well as a function call, which might add some noticeable overhead. Not considering your changes, I had already tested small buffers. At less than 512 bytes there was no measurable regression (there was one extra condition check) and for 512+ bytes it moved from no regression to some gains between 512 and 4096 bytes. Assuming you introduced no extra function calls, it should be the same. > I forgot to mention that I also want to understand whether we can actually > assume availability of XGETBV when CPUID says we support AVX512: You cannot assume as there are edge cases where AVX-512 was found on system one during compile but it's not actually available in a kernel on a second system at runtime despite the CPU actually having the hardware feature. I will review the new patch to see if there are anything that jumps out at me. Thanks, Paul
