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

[Michael Niedermayer]

On Tue, Feb 12, 2013 at 06:30:15PM +0100, Michael Niedermayer wrote:
> On Tue, Feb 12, 2013 at 09:18:34AM -0800, Ronald S. Bultje wrote:
> > Hi,
> > 
> > On Tue, Feb 12, 2013 at 9:05 AM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > > 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 ...
> > 
> > Isn't that the case already? The non-init code in
> > update_thread_context() for mpeg and h264 100% depends on ordering of
> > the fields, any field ordering change will break the threading.
> 
> yes, the problem exists already with some fields

also what i forgot, iam happy to add these comments/documentation to
the struct/fields myself if you prefer ...

[...]


-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

There will always be a question for which you do not know the correct answer.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20130213/58af55a8/attachment.asc>