Re: shapeit4 and AVX2
Dear Giulio,
I am CCing the public Debian Med mailing list and Michael Crusoe who
can help to improve the Debian package in order to have an AVX2 binary
optimized.
Le jeu. 5 nov. 2020 à 15:20, Giulio Genovese
<giulio.genovese@gmail.com> a écrit :
>
> I have noticed you are the author of the following patch for the shapeit4 debian package:
> https://salsa.debian.org/med-team/shapeit4/-/blob/master/debian/patches/use_shared_libs.patch
>
> I noticed that this causes shapeit4 to not use the AVX2 instruction set:
> -CXXFLAG=-O3 -mavx2 -mfma
> +#CXXFLAG=-O3 -mavx2 -mfma
> #Portable version without avx2 (much slower)
> -#CXXFLAG=-O3
> -LDFLAG=-O3
> +CXXFLAG=$(CPPFLAGS) $(CXXFLAGS) -O3
> +LDFLAG=$(LDFLAGS) -O3
>
> This causes shapeit4 to run significantly slower than it could on most systems where this package would be installed.
>
> I assume that the reason for this is that older CPUs do not support AVX2. Is it really important though to support these old systems? I doubt anybody would run such a tool on old machines. However, there might be reasons for this decision that I might be missing so I am curious to know the goals of this modification.
>
You are right, this is the Debian policy to provide binaries that
respect the architecture baseline [1] to support older CPUs. And you
are also right when you said nobody uses this tool on this kind of
outdated CPU. Personally, I don't have time to work on that but I
guess someone else in the Debian Med team would be interested?
Best,
Dylan
[1] https://wiki.debian.org/ArchitectureSpecificsMemo#amd64
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