Porting neon assembly to AdvSIMD Aarch64

[Sebastian Dröge]

On Mo, 2014-08-11 at 18:06 +0400, Ilya Palachev wrote:
> Hi, all.
> 
> Video and audio decoding for different formats in Gstreamer and its 
> plugins is highly optimized for arm architecture using NEON intrinsics 
> and direct ARMv7 NEON assembly .
> For different user applications such optimizations help to improve 
> performance.
> 
> I wonder whether anybody has tried to port such assembly to Aarch64 
> architecture.
> 
> At the beginning of 2014 the neon check has been disabled by William 
> Grant for aarch64 build to make possible the build of gstreamer for aarch64.
> https://bugzilla.gnome.org/show_bug.cgi?id=712367
> 
> And here - https://bugzilla.gnome.org/show_bug.cgi?id=722091 - Peter 
> Robinson has said that
> 
> In theory the aarch64 NEON implementation is backwards compatible with 
> ARMv7 NEON
> 
> It's not completely true. Armv8-a architecture is backwards compatible 
> with armv7l only at application level (Aarch32 execution mode).
> That means that if we have Aarch64 OS with firmware that provides the 
> set of libraries that the application "X" depends on: compiled both for 
> armv7l and aarch64, and we have to versions of application "X": for 
> arvm7l and aarch64, then you can launch both these applications (in 
> different processes). But it's impossible to run arvm7l code during the 
> execution of the aarch64 code. It requires the change of the exception 
> level (see official documentation).
> 
> So the question is:
> Does the development plan of gstreamer include such porting to aarch64, 
> since it's needed for better performance?

Hi,

I'm not aware of anybody porting the few bits of ARM assembly in
GStreamer to aarch64, or more importantly making ORC work on aarch64.
Can you file bug reports about all the cases that should be ported?
It's definitely something we should do, just needs someone with access
to appropriate hardware and time

-- 
Sebastian Dröge, Centricular Ltd - http://www.centricular.com
Expertise, Straight from the Source
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