[FFmpeg-devel] [PATCH]levc/hevc_cabac Optimise ff_hevc_hls_residual_coding (especially ARM)

[Christophe Gisquet]

Hi,

2016-01-22 14:29 GMT+01:00 John Cox <jc at kynesim.co.uk>:
>>This is a big slowdown on Win64 and UHD-bluray like sequences, but
>>that can be switched off in that case.
>
> I'm a bit surprised that it generated a big slowdown - some cache must
> be running just on the edge, but yes if you normally have hi-bitrate
> stuff then it isn't wanted.  On my test streams the bitrates were
> normally quite low - quite unlike what I would expect from blu-ray
> sequences.

Initial (4 sequences):
    6553 decicycles in g, 8387110 runs,   1498 skips
    5916 decicycles in g,33546118 runs,   8314 skips
    5028 decicycles in g,67101499 runs,   7365 skips
    4729 decicycles in g,33548420 runs,   6012 skips

Deactivating USE_N_END_1:
    4746 decicycles in g,16774296 runs,   2920 skips
    5373 decicycles in g,33545629 runs,   8803 skips
    4141 decicycles in g,67098928 runs,   9936 skips
    3869 decicycles in g,33544593 runs,   9839 skips

But I see the first one surprisingly having half the iterations (but
this has almost converged at this point).
So 10-20%.

I think it has more to do with cache pressure, both code, which
increases from 8 to 9.5KB, and data, with already "large" tables in a
loop that may need to tight.

> Default it to off on x86 but on on ARM?

Yes, I think so.

-- 
Christophe