Feedback-ID: ia2694551:Fastmail
Date: Fri, 26 Jan 2024 07:42:33 +0100
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: "Shankaran, Akash" <akash.shankaran@intel.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>,
	Noah Misch <noah@leadboat.com>, "Amonson, Paul D" <paul.d.amonson@intel.com>,
	Tom Lane <tgl@sss.pgh.pa.us>,
 Matthias van de Meent <boekewurm+postgres@gmail.com>,
	"pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Subject: Re: Popcount optimization using AVX512
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On 2024-Jan-25, Alvaro Herrera wrote:

> Finally, the matter of using ifunc as proposed by Noah seems to be still
> in the air, with no patches offered for the popcount family.

Oh, I just realized that the patch as currently proposed is placing the
optimized popcount code in the path that does not require going through
a function pointer.  So the performance increase is probably coming from
both avoiding jumping through the pointer as well as from the improved
instruction.

This suggests that finding a way to make the ifunc stuff work (with good
performance) is critical to this work.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"The ability of users to misuse tools is, of course, legendary" (David Steele)
https://postgr.es/m/11b38a96-6ded-4668-b772-40f992132797@pgmasters.net