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

[Michael Niedermayer]

On Thu, Sep 09, 2010 at 12:23:41PM +0200, Janne Grunau wrote:
> On Wed, Sep 08, 2010 at 11:42:56PM +0200, Michael Niedermayer wrote:
> > On Wed, Sep 08, 2010 at 06:17:27PM +0200, Janne Grunau wrote:
> > > 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
> > 
> > >  swscale.h |    3 ++-
> > >  utils.c   |   22 +++++++++++++++++++++-
> > >  2 files changed, 23 insertions(+), 2 deletions(-)
> > > c54cc19db9288e0cce8f8de94ec509442ef9b369  swscale_runtime_cpu_detection.diff
> > > 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
> > >  
> > >  #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;
> > > +    }
> > 
> > update_flags_cpu() is called on each sws_getCachedContext() and redoing cpu
> > detect on each such calls seems hackish
> 
> changed see attached patch
> 
> > besides a AUTODETECT instead of FORCE would not break API
> 
> I guess I can live with AUTODETECT if the API change to AV_CPU_FLAG_ is
> ok (together with a change to AV_CPU_FLAG_FORCE).
> 
> Janne

>  swscale.h |    3 ++-
>  utils.c   |   33 ++++++++++++++++++++++++++++++++-
>  2 files changed, 34 insertions(+), 2 deletions(-)
> 867167f166c693349d2f63314c3e150ff2b725d1  swscale_runtime_cpu_detection2.diff
> diff --git a/libswscale/swscale.h b/libswscale/swscale.h
> index 4e11c9a..6423334 100644
> --- a/libswscale/swscale.h
> +++ b/libswscale/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_AUTO     0x00100000 //< auto detect CPU extensions
>  
>  #define SWS_MAX_REDUCE_CUTOFF 0.002
>  
> diff --git a/libswscale/utils.c b/libswscale/utils.c
> index e9400f8..00bd219 100644
> --- a/libswscale/utils.c
> +++ b/libswscale/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 +723,37 @@ 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

> +    static int cpuflags;

this should go in av_get_cpu_flags() not one use of it

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I have never wished to cater to the crowd; for what I know they do not
approve, and what they approve I do not know. -- Epicurus
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