Re: Popcount optimization using AVX512

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