Re: Popcount optimization using AVX512

From: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Nathan Bossart <nathandbossart(at)gmail(dot)com>, "Devulapalli, Raghuveer" <raghuveer(dot)devulapalli(at)intel(dot)com>, "Shankaran, Akash" <akash(dot)shankaran(at)intel(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Rowley <dgrowleyml(at)gmail(dot)com>, Ants Aasma <ants(dot)aasma(at)cybertec(dot)at>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, "Amonson, Paul D" <paul(dot)d(dot)amonson(at)intel(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Popcount optimization using AVX512
Date: 2024-07-31 01:05:18
Message-ID: CA+hUKG+iZe4kZB_XEZXeX8Xr_G4CPbZ_JbhRa3i47XSjfaNDfw@mail.gmail.com
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On Wed, Jul 31, 2024 at 12:50 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> It's one thing for the avx512 path to have that overhead, but it's
> particularly absurd for pg_popcount32/pg_popcount64, where
>
> a) The function call overhead is a larger proportion of the cost.
> b) the instruction is almost universally available, including in the
> architecture baseline x86-64-v2, which several distros are using as the
> x86-64 baseline.

FWIW, another recent thread about that:

https://www.postgresql.org/message-id/flat/CA%2BhUKGKS64zJezV9y9mPcB-J0i%2BfLGiv3FAdwSH_3SCaVdrjyQ%40mail.gmail.com

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