Date: Mon, 18 Mar 2024 22:16:01 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: John Naylor <johncnaylorls@gmail.com>
Cc: Ants Aasma <ants@cybertec.at>, pgsql-hackers@postgresql.org
Subject: Re: add AVX2 support to simd.h
Message-ID: <20240319031601.GA828141@nathanxps13>
References: 
 <CANWCAZZgOS+f2W8+bFwHjYYT-6Fx4yP6dFpUy4oLfbXSgfTKLw@mail.gmail.com>
 <20240108173715.GC2611898@nathanxps13>
 <CANWCAZYsnwxT2YjUQBWcc2QqOoE6xyEtTkqD6kw2pKCX1xevrg@mail.gmail.com>
 <20240109162009.GA3033933@nathanxps13>
 <CANWCAZbad=aZaMaJD4pphrYNQLsjBUHN5oJ=9zvb5abtOn9QSw@mail.gmail.com>
 <20240315174149.GA3837823@nathanxps13>
 <20240315194016.GA3896616@nathanxps13>
 <CANWCAZYa3gz0ms1mWuDpM1uMWtWined6bxr2HkCWRwQg9YveYw@mail.gmail.com>
 <20240319020341.GA823987@nathanxps13>
 <CANWCAZbY8fxmz6TRXmPz_s1VOZQQgTkfvayaXvWbqQnq2D849g@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: 
 <CANWCAZbY8fxmz6TRXmPz_s1VOZQQgTkfvayaXvWbqQnq2D849g@mail.gmail.com>
Archived-At: 
 <https://www.postgresql.org/message-id/20240319031601.GA828141%40nathanxps13>
Precedence: bulk

On Tue, Mar 19, 2024 at 10:03:36AM +0700, John Naylor wrote:
> I took a brief look, and 0001 isn't quite what I had in mind. I can't
> quite tell what it's doing with the additional branches and "goto
> retry", but I meant something pretty simple:

Do you mean 0002?  0001 just adds a 2-register loop for remaining elements
once we've exhausted what can be processed with the 4-register loop.

> - if short, do one element at a time and return

0002 does this.

> - if long, do one block unconditionally, then round the start pointer
> up so that "end - start" is an exact multiple of blocks, and loop over
> them

0002 does the opposite of this.  That is, after we've completed as many
blocks as possible, we move the iterator variable back to "end -
block_size" and do one final iteration to cover all the remaining elements.

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