| From: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
|---|---|
| To: | "Amonson, Paul D" <paul(dot)d(dot)amonson(at)intel(dot)com> |
| Cc: | David Rowley <dgrowleyml(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, "Shankaran, Akash" <akash(dot)shankaran(at)intel(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 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: | 2024-03-18 17:30:04 |
| Message-ID: | 20240318173004.GA361138@nathanxps13 |
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| Lists: | pgsql-hackers |
On Mon, Mar 18, 2024 at 11:20:18AM -0500, Nathan Bossart wrote:
> 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().
Here is a more fleshed-out version of what I believe David is proposing.
On my machine, the gains aren't quite as impressive (~8.8s to ~5.2s for the
test_popcount benchmark). I assume this is because this patch turns
pg_popcount() into a function pointer, which is what the AVX512 patches do,
too. I left out the 32-bit section from pg_popcount_fast(), but I'll admit
that I'm not yet 100% sure that we can assume we're on a 64-bit system
there.
IMHO this work is arguably a prerequisite for the AVX512 work, as turning
pg_popcount() into a function pointer will likely regress performance for
folks on systems without AVX512 otherwise.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
| Attachment | Content-Type | Size |
|---|---|---|
| 0001-inline-function-calls-in-pg_popcount-when-possible.patch | text/x-diff | 6.0 KB |
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