From: Michael Platzer via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>
To: "ffmpeg-devel@ffmpeg.org" <ffmpeg-devel@ffmpeg.org>
Cc: Michael Platzer <michael.platzer@axelera.ai>,
"remi@remlab.net" <remi@remlab.net>
Subject: [FFmpeg-devel] RISC-V vector DSP functions: Motivation for commit 446b009
Date: Fri, 19 Jan 2024 15:30:00 +0000
Message-ID: <DB8P194MB0839826005206AA13F7CA7AC97702@DB8P194MB0839.EURP194.PROD.OUTLOOK.COM> (raw)
Hi,
Commit 446b0090cbb66ee614dcf6ca79c78dc8eb7f0e37 by Remi Denis-Courmont has replaced RISC-V vector loads and stores with negative stride with vrgather (generalized permutation within vector registers) instructions in order to reverse the elements in a vector register. The commit message explains that this change was done, but it does not explain why.
I fail to see what could possibly have motivated this change. The RISC-V vector loads and stores support negative stride values for use cases such as this one. Using vrgather instead replaces the more specific operation with a more generic one, which is likely to be less performant on most HW architectures. In addition, it requires to setup an index vector, thus raising dynamic instruction count.
Could someone familiar with this change (perhaps Remi himself) please explain the motivation for this change?
Thanks,
Michael
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
next reply other threads:[~2024-01-19 15:30 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-19 15:30 Michael Platzer via ffmpeg-devel [this message]
2024-01-19 17:14 ` Rémi Denis-Courmont
2024-01-23 17:34 ` Michael Platzer via ffmpeg-devel
2024-01-23 18:02 ` Rémi Denis-Courmont
2024-07-06 12:05 ` Rémi Denis-Courmont
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=DB8P194MB0839826005206AA13F7CA7AC97702@DB8P194MB0839.EURP194.PROD.OUTLOOK.COM \
--to=ffmpeg-devel@ffmpeg.org \
--cc=michael.platzer@axelera.ai \
--cc=remi@remlab.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Git Inbox Mirror of the ffmpeg-devel mailing list - see https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
This inbox may be cloned and mirrored by anyone:
git clone --mirror https://master.gitmailbox.com/ffmpegdev/0 ffmpegdev/git/0.git
# If you have public-inbox 1.1+ installed, you may
# initialize and index your mirror using the following commands:
public-inbox-init -V2 ffmpegdev ffmpegdev/ https://master.gitmailbox.com/ffmpegdev \
ffmpegdev@gitmailbox.com
public-inbox-index ffmpegdev
Example config snippet for mirrors.
AGPL code for this site: git clone https://public-inbox.org/public-inbox.git