[FFmpeg-devel] [RFC] use av_get_cpu_flags for real runtime CPU detection in swscale

[Måns Rullgård]

Janne Grunau <janne-ffmpeg at jannau.net> writes:

> Hi,
>
> attached patch implements runtime CPU detection in libswscale. One minor
> problem is that it changes behaviour on existing code which sets
> individual flags but obviously not the new SWS_CPU_CAPS_FORCE. I think
> it's acceptable since the flags have no effect with
> !CONFIG_RUNTIME_CPUDETECT.
>
> Janne
> diff --git a/swscale.h b/swscale.h
> index 4e11c9a..ca63796 100644
> --- a/swscale.h
> +++ b/swscale.h
> @@ -30,7 +30,7 @@
>  #include "libavutil/avutil.h"
>
>  #define LIBSWSCALE_VERSION_MAJOR 0
> -#define LIBSWSCALE_VERSION_MINOR 11
> +#define LIBSWSCALE_VERSION_MINOR 12
>  #define LIBSWSCALE_VERSION_MICRO 0
>
>  #define LIBSWSCALE_VERSION_INT  AV_VERSION_INT(LIBSWSCALE_VERSION_MAJOR, \
> @@ -93,6 +93,7 @@ const char *swscale_license(void);
>  #define SWS_CPU_CAPS_ALTIVEC  0x10000000
>  #define SWS_CPU_CAPS_BFIN     0x01000000
>  #define SWS_CPU_CAPS_SSE2     0x02000000
> +#define SWS_CPU_CAPS_FORCE    0x00100000

What does the force flag mean?

>  #define SWS_MAX_REDUCE_CUTOFF 0.002
>
> diff --git a/utils.c b/utils.c
> index e9400f8..9375489 100644
> --- a/utils.c
> +++ b/utils.c
> @@ -44,6 +44,7 @@
>  #include "libavutil/avutil.h"
>  #include "libavutil/bswap.h"
>  #include "libavutil/pixdesc.h"
> +#include "libavutil/cpu.h"
>
>  unsigned swscale_version(void)
>  {
> @@ -722,7 +723,26 @@ static int handle_jpeg(enum PixelFormat *format)
>
>  static int update_flags_cpu(int flags)
>  {
> -#if !CONFIG_RUNTIME_CPUDETECT //ensure that the flags match the compiled variant if cpudetect is off
> +#if CONFIG_RUNTIME_CPUDETECT
> +    int cpuflags;
> +
> +    if (!(flags & SWS_CPU_CAPS_FORCE)) {
> +        flags &= ~(SWS_CPU_CAPS_MMX|SWS_CPU_CAPS_MMX2|SWS_CPU_CAPS_3DNOW|SWS_CPU_CAPS_ALTIVEC|SWS_CPU_CAPS_BFIN);
> +
> +        cpuflags = av_get_cpu_flags();
> +
> +        if (ARCH_X86 && cpuflags & AV_CPU_FLAG_MMX)
> +            flags |= SWS_CPU_CAPS_MMX;
> +        if (ARCH_X86 && cpuflags & AV_CPU_FLAG_MMX2)
> +            flags |= SWS_CPU_CAPS_MMX2;
> +        if (ARCH_X86 && cpuflags & AV_CPU_FLAG_3DNOW)
> +            flags |= SWS_CPU_CAPS_3DNOW;;
> +        if (ARCH_X86 && cpuflags & AV_CPU_FLAG_SSE2)
> +            flags |= SWS_CPU_CAPS_SSE2;
> +        if (ARCH_PPC && cpuflags & AV_CPU_FLAG_ALTIVEC)
> +            flags |= SWS_CPU_CAPS_ALTIVEC;

Why not change libswscale to use the AV_CPU_FLAG_ values directly?
That would avoid this mess entirely.

-- 
M?ns Rullg?rd
mans at mansr.com