[vlc-devel] [PATCH v3] picture: align pictures on 64 bytes

[Rémi Denis-Courmont]

No. The plane offset from the start of the buffer / the first plane will be a multiple of 512 maybe. But the plane alignment cannot be larger than the containing buffer alignment.

So we should probably align the allocation to at least 512 for consistency. IMO we should align to page size and forget about the problem going forward, as we can probably never align beyond that.

Le 12 novembre 2018 13:44:08 GMT+02:00, Steve Lhomme <robux4 at ycbcr.xyz> a écrit :
>On 12/11/2018 11:59, Rémi Denis-Courmont wrote:
>> As far as I am concerned, the picture buffer could and maybe should
>be 
>> page-aligned anyway. The real question is what the plane and scan
>line 
>> alignment should be, which this patch leaves entirely open.
>
>picture_Allocate() is called after picture_Setup() which aligns lines
>to 
>at least 32 bytes. Then the amount of lines is also made a multiple of 
>16. So all the planes are always aligned to 512 bytes.
>
>>
>> Le 12 novembre 2018 11:48:25 GMT+02:00, Francois Cartegnie 
>> <fcvlcdev at free.fr> a écrit :
>>
>>     Le 12/11/2018 à 09:39, Steve Lhomme a écrit :
>>
>>         Code relying on AVX-2 (like dav1d) cannot work without an
>>         alignment of 32 bytes at least. Even avcodec has a
>requirement
>>         of 64 (likely to get at least 32 on all planes). So it's
>>         probably time to upgrade. picture_Setup ensures a horizontal
>>         alignment to 32 bytes and a vertical to 16 bytes. So for all
>>         buffers allocated by the core, we have a size multiple of 512
>>         bytes. 
>>
>>
>>     Didn't we had an issue with some codec*filter*idontremember and
>anything
>>
>>         16 ? 
>>
>>
>> -- 
>> Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez 
>> excuser ma brièveté.
>>
>>
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