[FFmpeg-devel] swscale/arm/yuv2rgb: make the code bitexact with its aarch64 counter part

[Matthieu Bouron]

On Sun, Mar 27, 2016 at 5:58 PM, Matthieu Bouron <matthieu.bouron at gmail.com>
wrote:

>
>
> On Fri, Mar 25, 2016 at 11:45 PM, Matthieu Bouron <
> matthieu.bouron at gmail.com> wrote:
>
>> The following patchset aims to make bitexact the yuv->rgba armv7 neon
>> code path
>> with the aarch64 one. It also aims to make the two code bases as close as
>> possible.
>>
>> [PATCH 01/10] swscale/arm/yuv2rgb: remove 32bit code path
>>
>> The current 32bit code path which is unused is removed.
>>
>> [PATCH 06/10] swscale/arm/yuv2rgb: only process one line at a time
>>
>> The code process only one line at a time for the yuv420p,nv12 and nv21
>> formats
>> with no regression in performance observed on a rpi2 (I've even observed a
>> slight increase of performance for the nv12 and nv21 formats).
>>
>> [PATCH 10/10] swscale/arm/yuv2rgb: make the code bitexact with its
>>
>> The last patch of the serie makes the code bitexact with the aarch64
>> version.
>> The increase of precision (which introduces a performance loss) is
>> compensated
>> by a refactor/optimisation that saves quite a few mov,vdup and vqdmulh.
>>
>> ./ffmpeg_g -nostats -f lavfi -i
>> testsrc2=1920x1080:d=5,format=nv12,bench=start,format=bgra,bench=stop -f
>> null -
>>
>> without patchset :
>> [bench @ 0x3eb6a0] t:0.020660 avg:0.020813 max:0.039399 min:0.020605
>>
>> with patchset:
>> [bench @ 0xe5f6a0] t:0.018924 avg:0.019075 max:0.037472 min:0.01884
>
>
> I've managed tu run the code on a beagle bone black board, here are the
> results:
>
> nv12->bgra
> without patchset: [bench @ 0x1fc02d0] t:0.011618 avg:0.011743 max:0.032600
> min:0.011513
> with patches 01-06/10 applied: [bench @ 0x8052d0] t:0.013438 avg:0.013659
> max:0.034427 min:0.013411
> with patches 01-10/10 applied: [bench @ 0x1fbb2d0] t:0.012554 avg:0.012751
> max:0.034288 min:0.012523
>
> yuv420p->bgra
> without patchset: [bench @ 0x6d42d0] t:0.012954 avg:0.013159 max:0.033866
> min:0.012945
> with patches 01-06/10 applied: [bench @ 0x20172d0] t:0.015154 avg:0.015358
> max:0.036186 min:0.015134
> with patches 01-10/10 applied: [bench @ 0x1d162d0] t:0.014623 avg:0.014784
> max:0.035487 min:0.014568
>
> So it looks like processing one line at a time as negative effect on
> performance on this board (as opposed to the rpi2). I'll try to keep the
> two line processing code and post some result (so we can decide, which
> version to choose).
>

I've managed to update the patchset to keep processing two line at a time
for the nv12,nv21 and yuv420p formats, here are the results:

./ffmpeg_g -nostats -f lavfi -i
testsrc2=1920x1080:d=5,format=nv12,bench=start,format=bgra,bench=stop -f
null -

Beagle bone black:
without patchset: [bench @ 0x1fc02d0] t:0.011618 avg:0.011743 max:0.032600
min:0.011513
with patchset v1: [bench @ 0x1fbb2d0] t:0.012554 avg:0.012751 max:0.034288
min:0.012523
with patchset v2: [bench @ 0x10f92d0] t:0.011239 avg:0.011408 max:0.032124
min:0.011202

Nexus5:
without patchset: avg: ~2,869ms
with patchset v1: avg: ~3,008ms
with patchset v2: avg: ~2,702ms

RPI2:
without patchset: [bench @ 0x3eb6a0] t:0.020660 avg:0.020813 max:0.039399
min:0.020605
with patchset v1:  [bench @ 0xe5f6a0] t:0.018924 avg:0.019075 max:0.037472
min:0.01884
with patchset v2: [bench @ 0xc1b6a0] t:0.020999 avg:0.021203 max:0.052184
min:0.020768

Given the following the results, i will drop the current patchset and
submit another one (which keeps processing two lines at a time).

Matthieu