On Thu, 3 Nov 2016, Diego Biurrun wrote:
>On Thu, Nov 03, 2016 at 09:42:44PM +0100, Janne Grunau wrote:
>>On 2016-11-03 20:38:11 +0100, Diego Biurrun wrote:
>>> On Wed, Nov 02, 2016 at 07:24:03PM +0100, Janne Grunau wrote:
>>> > On 2016-11-02 15:29:34 +0100, Diego Biurrun wrote:
>>> > > On Wed, Nov 02, 2016 at 04:00:38PM +0200, Martin Storsjö wrote:
>>> > > > On Wed, 2 Nov 2016, Diego Biurrun wrote:
>>> > > > >On Wed, Nov 02, 2016 at 03:23:14PM +0200, Martin Storsjö wrote:
>>> > > > >>On Wed, 2 Nov 2016, Martin Storsjö wrote:
>>> > > > >>Technically, having a _neon prefix for them is wrong, but anything
else
>>> > > > >>(omitting these two while hooking up avg32/avg64 separately) is more
>>> > > > >>complication - although I'm open for suggestions on how to handle
it best.
>>> > > > >
>>> > > > >Where exactly is the complication? In the way you assign the function
>>> > > > >pointers in the init file?
>>> > > > > > > > Yes, it'd require splitting up those macros a bit;
>>either for assigning the
>>> > > > same function pointers, but with a different simd instruction set
suffix, or
>>> > > > for only assigning the avg function pointer for those sizes.
>>> > > > > > Try something like
>>> > > > > > #define ff_vp9_copy32_neon ff_vp9_copy32_aarch64
>>> > > #define ff_vp9_copy64_neon ff_vp9_copy64_aarch64
>>> > > > > > before the assignment macros. You don't have to somehow drop
>>some of the
>>> > > assignments in the macros then. There's precedent for this in some of
the
>>> > > x86 init files.
>>> > > > That only fixes the function names but not the cpu_flag based
>>assignment > > if I understand it correctly. And it is a little bit
>>silly since neon is > > not really optional on aarch64. At least in the
>>Application profile.
>>> > I forgot to say that ff_vp9_copy32_aarch64 and ff_vp9_copy64_aarch64
>>> should be assigned to the function pointer unconditionally before
>>> checking for neon support.
>>
>>unconditionally is not nice since we want to compare them to C in
>>checkasm. That's the reason why we have the otherwise pointless
>>AV_CPU_FLAG_ARMV8
>
>Unconditional in the aarch64 init function is not unconditional:
>
>libavcodec/foodsp.c:
> if (ARCH_AARCH64)
> init_aarch64(..);
>
>libavcodec/aarch64/foodsp_init.c:
> init_aarch64(..)
> {
> function.pointer = ff_vp9_copy32_aarch64;
>
> if (have_neon())
> something.else = ff_whatever;
>
>Anyway, you get the idea. Quite possibly I'm overlooking something
>and it does not work as I envision...
Yes, because as Janne said, in that case, you can't via cpuflags choose not
to use this function, and you can't benchmark against the C version in
checkasm, since the C version always gets overridden by this function,
regardless of cpuflags.
That's why we've introduced the flag AV_CPU_FLAG_ARMV8, and one should wrap
such functions within have_armv8(cpuflags) instead of have_neon(cpuflags).
