| From: | Ants Aasma <ants(dot)aasma(at)cybertec(dot)at> |
|---|---|
| To: | Nathan Bossart <nathandbossart(at)gmail(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, "Amonson, Paul D" <paul(dot)d(dot)amonson(at)intel(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Rowley <dgrowleyml(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, "Shankaran, Akash" <akash(dot)shankaran(at)intel(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, 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: | 2024-04-01 22:09:57 |
| Message-ID: | CANwKhkPqS+8n9cvXOiLf2Rw7cD8ZvWBhZk=t17fjd-q8YCng-Q@mail.gmail.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
On Tue, 2 Apr 2024 at 00:31, Nathan Bossart <nathandbossart(at)gmail(dot)com> wrote:
>
> On Tue, Apr 02, 2024 at 12:11:59AM +0300, Ants Aasma wrote:
> > What about using the masking capabilities of AVX-512 to handle the
> > tail in the same code path? Masked out portions of a load instruction
> > will not generate an exception. To allow byte level granularity
> > masking, -mavx512bw is needed. Based on wikipedia this will only
> > disable this fast path on Knights Mill (Xeon Phi), in all other cases
> > VPOPCNTQ implies availability of BW.
>
> Sounds promising. IMHO we should really be sure that these kinds of loads
> won't generate segfaults and the like due to the masked-out portions. I
> searched around a little bit but haven't found anything that seemed
> definitive.
Interestingly the Intel software developer manual is not exactly
crystal clear on how memory faults with masks work, but volume 2A
chapter 2.8 [1] does specify that MOVDQU8 is of exception class E4.nb
that supports memory fault suppression on page fault.
Regards,
Ants Aasma
[1] https://cdrdv2-public.intel.com/819712/253666-sdm-vol-2a.pdf
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Nathan Bossart | 2024-04-01 22:11:17 | Re: Popcount optimization using AVX512 |
| Previous Message | Jacob Champion | 2024-04-01 22:07:45 | Re: [PoC] Federated Authn/z with OAUTHBEARER |