[FFmpeg-devel] [PATCH] avoid mb_xy recalculation in h264

[Alexander Strange]

On May 7, 2008, at 8:53 AM, Michael Niedermayer wrote:

> On Wed, May 07, 2008 at 03:05:47AM -0400, Alexander Strange wrote:
>> This line appears in a lot of h264.c functions:
>> const int mb_xy= s->mb_x + s->mb_y*s->mb_stride;
>>
>> It only changes once per MB, so we can add it to the context and only
>> recalculate it in decode_slice().
>> I put it at the end of H264Context, but it could be moved up  
>> earlier if
>> someone likes it there. The position doesn't seem to affect  
>> performance
>> much; it can't be moved next to mb_x/mb_y since that would put it in
>> MpegEncContext, and none of the other codecs use it.
>>
>> Patches:
>> 1- does that, updating it for MBAFF when needed
>> 2- removes some newly unused variables
>> 3- does the same thing to svq3.c
>>
>> Before: avg 8.799s max 8.8s min 8.794s
>> After: avg 8.645s max 8.651s min 8.641s
>
> Knowing the cpu and compiler would also be usefull.

gcc 4.0.1, core 2 x86-32 Darwin

I guess it's about the same as the usual distro compiler, but this  
isn't really a sensitive messing-with-the-register-allocator patch.


> [...]
>> @@ -6790,14 +6790,18 @@
>>
>>         for(;;){
>> //START_TIMER
>> -            int ret = decode_mb_cabac(h);
>> +            int ret;
>>             int eos;
>> +
>> +            h->mb_xy = s->mb_x + s->mb_y * s->mb_stride;
>> +            ret = decode_mb_cabac(h);
>> //STOP_TIMER("decode_mb_cabac")
>>
>>             if(ret>=0) hl_decode_mb(h);
>>
>>             if( ret >= 0 && FRAME_MBAFF ) { //FIXME optimal? or let  
>> mb_decode decode 16x32 ?
>>                 s->mb_y++;
>> +                h->mb_xy = s->mb_x + s->mb_y * s->mb_stride;
>>
>>                 if(ret>=0) ret = decode_mb_cabac(h);
>>
>> @@ -6830,12 +6834,17 @@
>>
>>     } else {
>>         for(;;){
>> -            int ret = decode_mb_cavlc(h);
>> +            int ret;
>> +
>> +            h->mb_xy = s->mb_x + s->mb_y * s->mb_stride;
>> +            ret = decode_mb_cavlc(h);
>>
>>             if(ret>=0) hl_decode_mb(h);
>>
>>             if(ret>=0 && FRAME_MBAFF){ //FIXME optimal? or let  
>> mb_decode decode 16x32 ?
>>                 s->mb_y++;
>> +                h->mb_xy = s->mb_x + s->mb_y * s->mb_stride;
>> +
>>                 ret = decode_mb_cavlc(h);
>
> the mb_xy init can be moved into decode_mb_ca*()

Done.


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