> -----Original Message-----
> From: Nathan Bossart <nathandbossart@gmail.com>
> Sent: Thursday, March 28, 2024 2:39 PM
> To: Amonson, Paul D <paul.d.amonson@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
512and 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
sayswe 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
availablein 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