On 9/4/2017 5:53 PM, Michael Niedermayer wrote:
> On Mon, Sep 04, 2017 at 09:27:32PM +0200, wm4 wrote:
>> On Mon, 4 Sep 2017 21:18:35 +0200
>> Michael Niedermayer <mich...@niedermayer.cc> wrote:
>>
>>> On Sat, Sep 02, 2017 at 09:47:38PM -0300, James Almer wrote:
>>>> From: Anton Khirnov <an...@khirnov.net>
>>>>
>>>> (cherry picked from commit e6bff23f1e11aefb16a2b5d6ee72bf7469c5a66e)
>>>> Signed-off-by: James Almer <jamr...@gmail.com>
>>>> ---
>>>> This is (afaics) the last API introduced to libav before the major bump.
>>>>
>>>> Now checking all the x86 flags that would require aligment of 16 bytes
>>>> or more.
>>>>
>>>> doc/APIchanges | 3 +++
>>>> libavutil/cpu.c | 35 +++++++++++++++++++++++++++++++++++
>>>> libavutil/cpu.h | 13 +++++++++++++
>>>> libavutil/version.h | 2 +-
>>>> 4 files changed, 52 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/doc/APIchanges b/doc/APIchanges
>>>> index 4effbf9364..6a57c210a9 100644
>>>> --- a/doc/APIchanges
>>>> +++ b/doc/APIchanges
>>>> @@ -15,6 +15,9 @@ libavutil: 2015-08-28
>>>>
>>>> API changes, most recent first:
>>>>
>>>> +2017-09-xx - xxxxxxx - lavu 55.75.100 / lavu 55.31.0 - cpu.h
>>>> + Add av_cpu_max_align() for querying maximum required data alignment.
>>>> +
>>>> 2017-09-01 - xxxxxxx - lavf 57.81.100 - avio.h
>>>> Add avio_read_partial().
>>>>
>>>> diff --git a/libavutil/cpu.c b/libavutil/cpu.c
>>>> index a22da0fa8c..4f04da2460 100644
>>>> --- a/libavutil/cpu.c
>>>> +++ b/libavutil/cpu.c
>>>> @@ -16,9 +16,11 @@
>>>> * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
>>>> 02110-1301 USA
>>>> */
>>>>
>>>> +#include <stddef.h>
>>>> #include <stdint.h>
>>>> #include <stdatomic.h>
>>>>
>>>> +#include "attributes.h"
>>>> #include "cpu.h"
>>>> #include "cpu_internal.h"
>>>> #include "config.h"
>>>> @@ -299,3 +301,36 @@ int av_cpu_count(void)
>>>>
>>>> return nb_cpus;
>>>> }
>>>> +
>>>> +size_t av_cpu_max_align(void)
>>>> +{
>>>> + int av_unused flags = av_get_cpu_flags();
>>>> +
>>>> +#if ARCH_ARM || ARCH_AARCH64
>>>> + if (flags & AV_CPU_FLAG_NEON)
>>>> + return 16;
>>>> +#elif ARCH_PPC
>>>> + if (flags & AV_CPU_FLAG_ALTIVEC)
>>>> + return 16;
>>>> +#elif ARCH_X86
>>>> + if (flags & (AV_CPU_FLAG_AVX2 |
>>>> + AV_CPU_FLAG_AVX |
>>>> + AV_CPU_FLAG_FMA4 |
>>>> + AV_CPU_FLAG_FMA3))
>>>> + return 32;
>>>> + if (flags & (AV_CPU_FLAG_XOP |
>>>> + AV_CPU_FLAG_AESNI |
>>>> + AV_CPU_FLAG_SSE42 |
>>>> + AV_CPU_FLAG_SSE4 |
>>>> + AV_CPU_FLAG_SSSE3 |
>>>> + AV_CPU_FLAG_SSE3 |
>>>> + AV_CPU_FLAG_SSE2 |
>>>> + AV_CPU_FLAG_SSE |
>>>> + AV_CPU_FLAG_AVXSLOW |
>>>> + AV_CPU_FLAG_SSE3SLOW |
>>>> + AV_CPU_FLAG_SSE2SLOW))
>>>> + return 16;
>>>> +#endif
>>>> +
>>>> + return 8;
>>>> +}
>>>> diff --git a/libavutil/cpu.h b/libavutil/cpu.h
>>>> index de05593446..9e5d40affe 100644
>>>> --- a/libavutil/cpu.h
>>>> +++ b/libavutil/cpu.h
>>>> @@ -21,6 +21,8 @@
>>>> #ifndef AVUTIL_CPU_H
>>>> #define AVUTIL_CPU_H
>>>>
>>>> +#include <stddef.h>
>>>> +
>>>> #include "attributes.h"
>>>>
>>>> #define AV_CPU_FLAG_FORCE 0x80000000 /* force usage of selected flags
>>>> (OR) */
>>>
>>>
>>>> @@ -113,4 +115,15 @@ int av_parse_cpu_caps(unsigned *flags, const char *s);
>>>> */
>>>> int av_cpu_count(void);
>>>>
>>>> +/**
>>>> + * Get the maximum data alignment that may be required by FFmpeg.
>>>> + *
>>>> + * Note that this is affected by the build configuration and the CPU
>>>> flags mask,
>>>> + * so e.g. if the CPU supports AVX, but libavutil has been built with
>>>> + * --disable-avx or the AV_CPU_FLAG_AVX flag has been disabled through
>>>> + * av_set_cpu_flags_mask(), then this function will behave as if AVX is
>>>> not
>>>> + * present.
>>>> + */
>>>> +size_t av_cpu_max_align(void);
>>>
>>> This might interact badly with runtime cpu flags/mask changes
>>>
>>> If its used to choose the alignment for allocated frames and
>>> after some are allocated the cpu flags are changed there could be
>>> still frames in queues that may not have sufficient alignment for the
>>> new flags
>>
>> There's no such thing as runtime CPU flag changes.
>
> We even have an API to change the cpu flags at runtime.
>
> av_set_cpu_flags_mask() and av_force_cpu_flags()
>
> There is no restriction in the API on when they can be called.
>
> you can call av_force_cpu_flags(0) then open a decoder then call
> av_force_cpu_flags(AV_CPU_FLAG_MMX|AV_CPU_FLAG_SSE)
> then open a filter or encoder
> then run the code and it could crash as the allocated frames from
> earlier are not aligned enough for the 2nd filter or encoder
>
> There also may be other scenarios where this can occur
Alright, I just arrived to this cherry pick during merges. So my
question is, do i apply it and skip the commit that makes use of it to
choose alignment within ffmpeg?
Even if unused at first, I'd rather not skip its addition.
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