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

Matthieu Bouron matthieu.bouron at gmail.com
Fri Apr 1 16:15:34 CEST 2016


On Mon, Mar 28, 2016 at 9:12 PM, Matthieu Bouron <matthieu.bouron at gmail.com>
wrote:

>
>
> 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).
>

I will push the updated patchset (which takes into account Benoit's
comments) in one hour~.

Matthieu


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