Re: F39 proposal: RPM 4.19 (System-Wide Change proposal)

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On Tue, Apr 04, 2023 at 07:37:59AM +0000, Zbigniew Jędrzejewski-Szmek wrote:
> On Sun, Apr 02, 2023 at 09:54:04PM +0200, Dan Čermák wrote:
> > The only benchmark that *I* am aware of is this one done by Martin
> > Jambor: https://jamborm.github.io/spec-2022-07-29-levels/
> 
> This is very … underwhelming. x86-64-v2 is essentially identical to x86-64-v1.
> x86-64-v3 is better. It even shows speed-ups of 20%, but only with -Ofast.
> And -Ofast is not something that can be enabled as a default build flag,
> because it leads to surprising and unpredictable behaviour in some cases. (*)
> At -O2, which we use, the speed up is maybe 10%.

Given that GCC 12 and later autovectorizes at -O2, it might be more than
10%.

> > tl;dr; v2 does not really bring notable improvements, only v3 but also
> > only in some selected synthetic benchmarks.
> > 
> > openSUSE Tumbleweed went a different route and chose to utilize
> > glibc-hwcaps instead:
> > https://en.opensuse.org/openSUSE:X86-64-Architecture-Levels
> > https://lists.opensuse.org/archives/list/factory@xxxxxxxxxxxxxxxxxx/thread/ZOHLT4CQ7TDOJJ2VV7HKMN5G2MR2CTMD
> 
> Yeah, I think that's the way to go. I think we should identify 100
> shared libraries which would be positively impacted by x86-64-v3
> and provide a -v3 subrpm for them. This would be a nice feature for
> F40.

Why a subrpm?  Should be possible to just arrange for one src.rpm to
build the library twice and install the x86-64-v3 into
/usr/lib64/glibc-hwcaps/x86-64-v3/
Perhaps come with some macro to simplify that for packagers.

	Jakub
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