daxpy 10x slower on macOS (Haswell)

[simonbyrne]

Calls to daxpy seem to be about 10x slower on macOS than when run inside a Linux VM on the same machine (both give the config as "USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell").

This affects a lot of code which depends on it (e.g. dgebrd).

downstream: JuliaLang/LinearAlgebra.jl#501

[martin-frbg]

Nobody here currently has a Mac I fear. From anecdotal evidence in previous issues (#730, JuliaLang/julia#901) you could try removing the .align 16 in kernel/x86_64/daxpy_microk_haswell-2.c, or try with the current "develop" tree as that happens to have that microkernel replaced with the non-AVX2 Sandybridge one for unrelated reasons (the respective microkernel is #included at the top of kernel/x86_64/daxpy.c)

[brada4]

Can you check if virtual machine has AVX2 inside in /proc/cpuinfo (i.e haswell or sandybridge is used)

[simonbyrne]

Can you check if virtual machine has AVX2 inside in /proc/cpuinfo (i.e haswell or sandybridge is used)

Yes, it does.

[simonbyrne]

Using the current develop branch (e3a80e6) doesn't fix it either.

[martin-frbg]

Does killing any and all .align16 in the daxpy microkernel file change anything ?

[simonbyrne]

Yes, commenting that out in daxpy_microk_sandy-2.c seems to fix it.

[ViralBShah]

Is it possible to perhaps have a new release once we fix this, given that we haven't had one for a long time? We're happy (in the Julia community) to try out an RC and give feedback before release.

[simonbyrne]

Ah, does it have anything to do with this commit comment?

According to the Mac developer docs:

align_expression is a power of 2 between 0 and 15 (for example, the argument of .align 3 means 2 ^ 3 (8)–byte alignment)

As I understand, p2align should be consistent across platforms.

[martin-frbg]

@simonbyrne yes, sorry for not digging down to the original source earlier. And thanks for the pointer to p2align, certainly looks cleaner than adding ifdefs around each and every .align (though the underlying issue seems to be an Apple flaw, if their align is identical to p2align).
@ViralBShah I hope so, but xianyi has not been seen here for quite some time, and I still believe only he can do releases

[simonbyrne]

No worries. Thanks for all your effort maintaining OpenBLAS.

[ViralBShah]

Thank you. We might just apply the patch for now in that case.

[ViralBShah]

I have emailed @xianyi about adding more people as admin and perhaps even moving the project to an OpenBLAS organization to help maintain it better.

[martin-frbg]

PR merged for Haswell and Sandybridge, from wikipedia I suspect Nehalem may also be needed for 2010-12 models of Mac Pro and iMac ?