[flac-dev] Performance checks

[Janne Hyvärinen]

On 31.5.2013 13:04, Miroslav Lichvar wrote:
> On Wed, May 29, 2013 at 04:08:57PM +0200, Martijn van Beurden wrote:
>> I was surprised to see that the Windows compile on wine actually
>> outperformed the native Linux one. Probably GCC 4.6 optimized a little
>> better or something very weird is going on in wine, I don't know. The
>> assembly optimizations work very well on encoding, but actually slow
>> things down when decoding. The difference is not very large however.
> In a quick test with a pre 4.8 gcc on a Core 2 CPU I see a small
> improvement in decoding speed with assembly optimizations turned on,
> but I think the difference used to be larger. Perhaps the compilers
> got better or MMX is slower relative to normal code on current CPUs.
>
> Disabling the FLAC__bitreader_read_rice_signed_block_asm_ia32_bswap
> function seems to help a bit. (there is an #if disabling the function
> with comment "OPT: not clearly faster, needs more testing" in the
> src/libFLAC/stream_decoder.c file)
>
> Here is the relative decoding speed with -5 and -8:
> 			-5		-8
> no asm			99.0%		97.0%
> asm			100.0%		100.0%
> asm (no ia32_bswap)	102.7%		102.7%
>
> I think we should drop that assembly function as the C
> version seems to be faster now.
>
> Can anyone confirm this?
>
> Thanks,
>

I can confirm. I see 10% speed improvement with that change on Core i7.
Decoding a 1h18min38.133s long test FLAC -8 encoded file takes with 
normal asm optimizations 7.656s (speed: 616,266x realtime) and with that 
tiny change 6.937s (speed: 680,140x realtime).