Hi,
For reference, the C++ implementation is compiled by default with SSE4.2
enabled. We had some rare bug reports of people using very old CPUs
where Arrow C++ would crash (for example for lack of POPCNT instruction,
which is very useful for fast null count computation).
We also have some dynamic dispatch for select routines where AVX2 or
AVX512 paths are available.
AVX2 by default is probably too contentious for the time being, IMHO.
Regards
Antoine.
Le 07/01/2023 à 13:08, Raphael Taylor-Davies a écrit :
Hi,
It is fairy common to see binaries in the wild making use of the Rust
arrow libraries compiled with extremely limited SIMD support enabled. As
I imagine others in the community have run into this before, I thought
I'd send an email to solicit thoughts.
There are a couple of things that make the Rust implementation
particularly susceptible to this problem:
- Rust lacks a stable ABI, and so all builds are from source
- The default x86 release target lacks even SSE3 support (released 2004)
let alone anything more modern
- The Rust implementation relies on LLVM to generate vectorised code,
there are no stable SIMD intrinsics and may never be
My suggestion in [1] is to generate a compilation error if building a
release binary without SSE3 enabled. This provides a very low barrier to
entry, and guides users towards the "right thing". In practice I suspect
most users will be able to add `target-cpu=haswell` and benefit from
everything up to and including AVX2.
An alternative proposal would be to auto-select from multiple
implementations at runtime, however, this will effectively multiply
executable size and compile times, which are already problematic, by
each combination of features. It is tractable, but I feel optimising for
a very rare breed of user that is running high-performance CPU workloads
on a CPU from more than a decade ago... I'm not sure what other people
think?
Any and all feedback welcome, preferably on the linked issue [1] to keep
things in one place.
Kind Regards,
Raphael Taylor-Davies
[1]: https://github.com/apache/arrow-rs/issues/3485
