Date: Mon, 18 Mar 2024 11:20:18 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: "Amonson, Paul D" <paul.d.amonson@intel.com>
Cc: David Rowley <dgrowleyml@gmail.com>, Andres Freund <andres@anarazel.de>,
	Alvaro Herrera <alvherre@alvh.no-ip.org>,
	"Shankaran, Akash" <akash.shankaran@intel.com>,
	Noah Misch <noah@leadboat.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
Message-ID: <20240318162018.GA204772@nathanxps13>
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On Mon, Mar 18, 2024 at 04:07:40PM +0000, Amonson, Paul D wrote:
> Won't I still need the runtime checks? If I compile with a compiler
> supporting the HW "feature" but run on HW without that feature,  I will
> want to avoid faults due to illegal operations. Won't that also affect
> performance?

I don't think David was suggesting that we need to remove the runtime
checks for AVX512.  IIUC he was pointing out that most of the performance
gain is from removing the function call overhead, which your v8-0002 patch
already does for the proposed AVX512 code.  We can apply a similar
optimization for systems without AVX512 by inlining the code for
pg_popcount64() and pg_popcount32().

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com