Date: Mon, 11 Mar 2024 20:34:36 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: "Amonson, Paul D" <paul.d.amonson@intel.com>
Cc: 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: <20240312013436.GA1787866@nathanxps13>
References: <BL1PR11MB53046A243932039BD545EBF4DC592@BL1PR11MB5304.namprd11.prod.outlook.com>
 <20240301214457.GA3024365@nathanxps13>
 <BL1PR11MB5304BFE26BAC25624508CFD2DC232@BL1PR11MB5304.namprd11.prod.outlook.com>
 <20240304222118.GB3367383@nathanxps13>
 <BL1PR11MB53047C28DDBA6A2E77B9420ADC222@BL1PR11MB5304.namprd11.prod.outlook.com>
 <20240305163730.GA3479896@nathanxps13>
 <BL1PR11MB530444AEE08A91242ABA1915DC222@BL1PR11MB5304.namprd11.prod.outlook.com>
 <20240307173318.GA455851@nathanxps13>
 <20240307213600.GA563369@nathanxps13>
 <BL1PR11MB5304165E7A81E0107E70B069DC242@BL1PR11MB5304.namprd11.prod.outlook.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <BL1PR11MB5304165E7A81E0107E70B069DC242@BL1PR11MB5304.namprd11.prod.outlook.com>
Archived-At: <https://www.postgresql.org/message-id/20240312013436.GA1787866%40nathanxps13>
Precedence: bulk

On Mon, Mar 11, 2024 at 09:59:53PM +0000, Amonson, Paul D wrote:
> I will be splitting the request into 2 patches. I am attaching the first
> patch (refactoring only) and I updated the commitfest entry to match this
> patch. I have a question however:
> Do I need to wait for the refactor patch to be merged before I post the
> AVX portion of this feature in this thread?

Thanks.  There's no need to wait to post the AVX portion.  I recommend
using "git format-patch" to construct the patch set for the lists.

>> Apologies for harping on this, but I'm still not seeing the need for these
>> SIZEOF_VOID_P changes.  While it's unlikely that this makes any practical
>> difference, I see no reason to more strictly check SIZEOF_VOID_P here.
> 
> I got rid of the second occurrence as I agree it is not needed but unless
> you see something I don't how to know which function to call between a
> 32-bit and 64-bit architecture? Maybe I am missing something obvious?
> What exactly do you suggest here? I am happy to always call either
> pg_popcount32() or pg_popcount64() with the understanding that it may not
> be optimal, but I do need to know which to use.

I'm recommending that we don't change any of the code in the pg_popcount()
function (which is renamed to pg_popcount_slow() in your v6 patch).  If
pointers are 8 or more bytes, we'll try to process the buffer in 64-bit
chunks.  Else, we'll try to process it in 32-bit chunks.  Any remaining
bytes will be processed one-by-one.

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