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costel78
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Joined: 20 Apr 2007
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 Posted: Mon Jan 25, 2021 3:16 pm Post subject: arm64 neon cpu flag status |
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It is been a year since
| Code: | # Aaron Bauman <bman@gentoo.org> (2019-12-27)
# Mask cpu_flags_arm_neon for all of arm64
# A neon64 USE is being discussed
cpu_flags_arm_neon |
Especially on tls I get lower output on arm64 compared to 32 bits arm.
Is there any progress or workaround ?
Why neon was disabled in first place ? Raspberry Pi 4 support neon instructions. Does SIMD include NEON on arm64 ?
Thank you!
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NeddySeagoon
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| Posted: Mon Jan 25, 2021 4:55 pm Post subject: |
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costel78,
affects assembly code inserts that some packages provide.
It does not affect the instruction stream emitted by gcc.
cpu_flags_arm_neon is used by | Code: | $ equery h cpu_flags_arm_neon
* Searching for USE flag cpu_flags_arm_neon ...
[IP-] [ ] dev-libs/nettle-3.7:0/8-6
[IP-] [ ] mail-client/thunderbird-78.6.0:0/78
[IP-] [ ] media-libs/graphene-1.10.2:0
[IP-] [ ] media-libs/libaom-2.0.0:0/2
[IP-] [ ] media-libs/libpng-1.6.37-r2:0/16
[IP-] [ ] media-libs/libwebp-1.1.0:0/7
[IP-] [ ] media-libs/openh264-2.1.1:0/6
[IP-] [ ] media-libs/opus-1.3.1-r1:0
[IP-] [ ] media-libs/x265-3.4:0/192
[IP-] [ ] media-video/ffmpeg-4.3.1:0/56.58.58
[IP-] [ ] media-video/vlc-3.0.12.1-r100:0/5-9
[IP-] [ ] www-client/firefox-84.0.2:0/84
[IP-] [ ] x11-libs/pixman-0.40.0:0 |
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NeddySeagoon
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costel78
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Joined: 20 Apr 2007
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| Posted: Tue Jan 26, 2021 8:46 pm Post subject: |
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Oh, I see. I have to better document myself.
Do you know why the flag have been disabled ?
Thank you!
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NeddySeagoon
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| Posted: Tue Jan 26, 2021 9:29 pm Post subject: |
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costel78,
neon is a 32 bit instruct set as far as I know.
On arm64, the 32 bit instruction set is optional. The Pi4 and 4 have it, the Cavium Thunder does not.
Its not possible to mix 32 bit and 64 bit instructions on arm64.
There is no multilib on on 64 either, so running 32 bit programs on arm64 is not possible, even if the silicon has 32 bit support.
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NeddySeagoon
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costel78
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Joined: 20 Apr 2007
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| Posted: Wed Jan 27, 2021 6:34 am Post subject: |
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That was what I was reading. But the announce contain "# A neon64 USE is being discussed" which is misleading, it seems.
Everything is clear now.
Thank you very much for explanations!
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Gentoo on ARM
