On Sat, May 17, 2025 at 3:00 PM <m...@astro.utoronto.ca> wrote:

> Hi Sayed,
>
> I'm a bit confused: does your suggested change mean that prre-2009
> processors won't work at all, or that no use will be made of the (little)
> acceleration that they provided?  The latter seems fine, but not working at
> all seems rather bad.


I don't think it's that bad. It's always a tradeoff between performance,
binary size, effort, and compatibility. We've had this discussion before,
e.g. when moving to SSE3 as the baseline, and decided that we should not
drop support for a feature if less than 99.5% of CPUs in the wild has
support, but if it's above we can do it. Previous bumps have not given any
significant pushback from our user base.

>From https://github.com/numpy/numpy/issues/27851, half a year ago:

*The most widely used data source for determining what hardware is out
there is, I believe,
https://store.steampowered.com/hwsurvey/?platform=combined
<https://store.steampowered.com/hwsurvey/?platform=combined>. That
currently says that SSE3 is at 100%, SSE4.1 at 99.78% and SSE4.2 at 99.70%.
Meaning that if we bump the baseline up to SSE4.2, we'd only be dropping
support for ~0.3% of systems with really old CPUs.*

SSE 4.2 support as of today increased to 99.78%, so the number of CPUs we'd
drop support for moved from 0.3% to 0.22% in 6 months. That means we're
still being very conservative after this bump, IIRC more so than when we
dropped support for CPUs without SSE3.

Cheers,
Ralf



> Though I'd think that for any old processors one can just fall back to the
> standard `libm` implementations.
>
> All the best,
>
> Marten
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