Re: Changing default -march landscape

On Thu, Jun 13, 2024 at 01:20:17PM +1200, Thomas Munro wrote:
> The way I think about it, it's not our place to require anything (I
> mean, we can't literally put -march=XXX into our build files, or if we
> do the Debian et al maintainers will have to remove them by local
> patch because they are in charge of what the baseline is for their
> distro), but we should do the best thing possible when people DO build
> with modern -march. I would assume for example that Amazon Linux is
> set up to use a default -march that targets the actual minimum
> microarch level on AWS hosts. I guess what I'm pointing out here is
> that the baseline is (finally!) moving on common distributions, and
> yet we've coded things in a way that doesn't benefit...

That's true, but my point is that as soon as we start avoiding function
pointers more commonly, it becomes difficult to justify adding them back in
order to support new instruction sets. Should we just compile in the SSE
4.2 version, or should we take a chance on AVX-512 with the function
pointer?

>> The idea that's been floating around recently is to build a bunch of
>> different versions of Postgres and to choose one on startup based on what
>> the CPU supports. That seems like quite a lot of work, and it'll increase
>> the size of the builds quite a bit, but it at least doesn't have the
>> aforementioned problem.
>
> I guess another idea would be for the PGDG packagers or someone else
> interested in performance to create repos with binaries built for
> these microarch levels and users can research what they need. The new
> -v2 etc levels are a lot more practical than the microarch names and
> individual features...

Heartily agreed.

--
nathan