[FFmpeg-devel] [PATCH] h264: remove clear_blocks call in threading init.

[Michael Niedermayer]

On Mon, Feb 11, 2013 at 06:08:45PM -0800, Ronald S. Bultje wrote:
> From: "Ronald S. Bultje" <rsbultje at gmail.com>
> 
> Init code in that if statement goes down from 26716 cycles to 26047
> cycles, i.e. the removal of the clear_blocks and smaller memcpy()
> together save around 670 cycles.
> ---
>  libavcodec/h264.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/libavcodec/h264.c b/libavcodec/h264.c
> index 2d6c5e6..994e002 100644
> --- a/libavcodec/h264.c
> +++ b/libavcodec/h264.c
> @@ -1253,7 +1253,9 @@ static int decode_update_thread_context(AVCodecContext *dst,
>  
>          // copy all fields after MpegEnc
>          memcpy(&h->s + 1, &h1->s + 1,
> -               sizeof(H264Context) - sizeof(MpegEncContext));
> +               offsetof(H264Context, intra_gb) - sizeof(MpegEncContext));
> +        memcpy(&h->cabac, &h1->cabac,
> +               sizeof(H264Context) - offsetof(H264Context, cabac));
>          memset(h->sps_buffers, 0, sizeof(h->sps_buffers));
>          memset(h->pps_buffers, 0, sizeof(h->pps_buffers));
>  

If either of these fields is moved in the structure or a new field
added between then threading can mysteriously break.
also the comment above would not match the code anymore
iam not sure this is a good idea but if it is done then the fields
should be documented in the struct so a developer touching them would
know they are special ...


[...]

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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In fact, the RIAA has been known to suggest that students drop out
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