[FFmpeg-devel] [PATCH 05/11] avcodec: add stride alignment needed for AVX-512

James Almer jamrial at gmail.com
Fri Nov 10 16:21:00 EET 2017


On 11/10/2017 10:58 AM, James Darnley wrote:
> On 2017-11-10 02:38, James Almer wrote:
>> On 11/9/2017 8:58 AM, James Darnley wrote:
>>> ---
>>>  configure             | 2 ++
>>>  libavcodec/internal.h | 4 +++-
>>>  2 files changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/configure b/configure
>>> index 146a87324c..fce8030d91 100755
>>> --- a/configure
>>> +++ b/configure
>>> @@ -1886,6 +1886,7 @@ ARCH_FEATURES="
>>>      local_aligned
>>>      simd_align_16
>>>      simd_align_32
>>> +    simd_align_64
>>>  "
>>>  
>>>  BUILTIN_LIST="
>>> @@ -2385,6 +2386,7 @@ fast_clz_if_any="aarch64 alpha avr32 mips ppc x86"
>>>  fast_unaligned_if_any="aarch64 ppc x86"
>>>  simd_align_16_if_any="altivec neon sse"
>>>  simd_align_32_if_any="avx"
>>> +simd_align_64_if_any="avx512"
>>>  
>>>  # system capabilities
>>>  symver_if_any="symver_asm_label symver_gnu_asm"
>>> diff --git a/libavcodec/internal.h b/libavcodec/internal.h
>>> index 7748f09f54..84070431ed 100644
>>> --- a/libavcodec/internal.h
>>> +++ b/libavcodec/internal.h
>>> @@ -87,7 +87,9 @@
>>>  
>>>  #define FF_SIGNBIT(x) ((x) >> CHAR_BIT * sizeof(x) - 1)
>>>  
>>> -#if HAVE_SIMD_ALIGN_32
>>> +#if HAVE_SIMD_ALIGN_64
>>> +#   define STRIDE_ALIGN 64 /* AVX-512 */
>>> +#elif HAVE_SIMD_ALIGN_32
>>>  #   define STRIDE_ALIGN 32
>>>  #elif HAVE_SIMD_ALIGN_16
>>>  #   define STRIDE_ALIGN 16
>>>
>>
>> LGTM, but I'd really like to find a way to start using
>> av_get_cpu_max_align() as it was meant to be done when it was
>> introduced, instead of keeping hardcoding alignment based on configure
>> time options.
> 
> That sounds like a good idea to me.  If time allows I will try to start
> a discussion about it.  It sounds ripe for a lot of bikeshedding :)
> 
>> Maybe adding a line to the av_force_cpu_flags() and
>> av_set_cpu_flags_mask() doxy stating you should reinit all your decoder
>> and encoder contexts after calling them or similar.
> 
> Did you want me to add that one of my patches?

No, it's unrelated to this set. It was a suggestion to solve the above
issue. this patch is good as is while that's discussed.


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