Re: [PATCH] SVE popcount support

Chiranmoy.Bhattacharya@fujitsu.com <chiranmoy.bhattacharya@fujitsu.com>

From: "Chiranmoy.Bhattacharya@fujitsu.com" <Chiranmoy.Bhattacharya@fujitsu.com>

To: Nathan Bossart <nathandbossart@gmail.com>

Cc: "Malladi, Rama" <ramamalladi@hotmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, "Ragesh.Hajela@fujitsu.com" <Ragesh.Hajela@fujitsu.com>, Salvatore Dipietro <dipiets@amazon.com>, "Devanga.Susmitha@fujitsu.com" <Devanga.Susmitha@fujitsu.com>

Date: 2025-03-12T10:34:46Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Optimize popcount functions with ARM SVE intrinsics.
- 519338ace410 18.0 landed
Optimize popcount functions with ARM Neon intrinsics.
- 6be53c27673a 18.0 landed
Rename TRY_POPCNT_FAST to TRY_POPCNT_X86_64.
- 9ac6f7e7ceb6 18.0 landed

Attachments

v6-0001-SVE-and-NEON-support-for-popcount.patch (application/octet-stream) patch v6-0001

On Wed, Mar 12, 2025 at 02:41:18AM +0000, nathandbossart@gmail.com wrote:

> v5-no-sve is the result of using a function pointer, but pointing to the
> "slow" versions instead of the SVE version.  v5-sve is the result of the
> latest patch in this thread on a machine with SVE support, and v5-4reg is
> the result of the latest patch in this thread modified to process 4
> register's worth of data at a time.

Nice, I wonder why I did not observe any performance gain in the 4reg
version. Did you modify the 4reg version code?

One possible explanation is that you used Graviton4 based instances
whereas I used Graviton3 instances.

> For the latter point, I think we should consider trying to add a separate
> Neon implementation that we use as a fallback for machines that don't have
> SVE.  My understanding is that Neon is virtually universally supported on
> 64-bit Arm gear, so that will not only help offset the function pointer
> overhead but may even improve performance for a much wider set of machines.

I have added the NEON implementation in the latest patch.

Here are the numbers for drive_popcount(1000000, 1024) on m7g.8xlarge:
Scalar - 692ms
Neon - 298ms
SVE - 112ms

-Chiranmoy