[FFmpeg-soc] [soc]: r5419 - als/alsdec.c

[Thilo Borgmann]

Michael Niedermayer schrieb:
> On Wed, Oct 21, 2009 at 12:33:21PM +0200, Thilo Borgmann wrote:
>> Michael Niedermayer schrieb:
>>> On Tue, Oct 20, 2009 at 03:00:40PM +0200, thilo.borgmann wrote:
>>>> Author: thilo.borgmann
>>>> Date: Tue Oct 20 15:00:40 2009
>>>> New Revision: 5419
>>>>
>>>> Log:
>>>> Splits reading of block data and decoding of block data.
>>>> Introduces ALSBlockData struct.
>>> You are missing the "why" part, that should be explained in the commit
>>> message
>> Yes, sorry.
>>
>>> also this needs a benchmark as there are many additional dereferences
>>> added
>> It is a necessary evil to support MCC. If it would be faster the "old"
>> way for non-MCC files, would this reason to have both, a split read &
>> decode function pair and an all-in-one function?
> 
> I think a benchmark is usefull to judge if we should spend time thinking
> about alternatives to the many dereferences or not
> 

The combined (old) function:

848450 dezicycles in combined, 1 runs, 0 skips
436625 dezicycles in combined, 2 runs, 0 skips
422562 dezicycles in combined, 4 runs, 0 skips
251822 dezicycles in combined, 8 runs, 0 skips
275631 dezicycles in combined, 16 runs, 0 skips
244726 dezicycles in combined, 32 runs, 0 skips
206217 dezicycles in combined, 64 runs, 0 skips
179422 dezicycles in combined, 119 runs, 9 skips
179422 dezicycles in combined, 119 runs, 137 skips

The separate (new) functions:

984100 dezicycles in separate, 1 runs, 0 skips
499555 dezicycles in separate, 2 runs, 0 skips
534420 dezicycles in separate, 4 runs, 0 skips
369905 dezicycles in separate, 8 runs, 0 skips
340817 dezicycles in separate, 16 runs, 0 skips
280026 dezicycles in separate, 32 runs, 0 skips
263883 dezicycles in separate, 64 runs, 0 skips
231872 dezicycles in separate, 119 runs, 9 skips
231872 dezicycles in separate, 119 runs, 137 skips

This is a 30% difference which makes me think to try these alternatives.

What comes into my mind would be to use local copies, thus dereferencing
the field of *bd just twice. One at the top and one at the bottom of the
function.

Anything else?

-Thilo