At least for now, I think I've done pretty much all I can do to optimize the JPEG codec. The latest round of optimizations in r3902 speed up the Huffman decoder by employing some of the same techniques I employed with the encoder, including register reduction, using a 64-bit holding register on 64-bit platforms, eliminating branches, etc. Unfortunately, due to the nature of Huffman decoding, the loop unrolling that I did with the encoder couldn't be done to the decoder (because the decoder dynamically alters the loop counter.) Some optimizations were borrowed from TurboJPEG/mediaLib, so these specific modifications are licensed under the wxWidgets Library License (GPL compatible.)
The attached spreadsheet shows where we stand, and a summary is included
below:
Relative performance to TurboJPEG/IPP (Neglecting Grayscale):
Pentium 4 Xeon/2.8 GHz/CentOS 4.7
Compress Decompress
64-bit: -18.6 to -5.23% -16.4 to +11.42%
32-bit: -39.1 to -20.8% -20.2 to +2.17%
AMD Athlon 64 X2 5050e/dual core/2.6 GHz/CentOS 5.3
Compress Decompress
64-bit: +4.45 to +11.4% -16.4 to +7.63%
32-bit: -18.1 to -8.16% -11.23 to +17.7%
Intel Core Duo/2.0 GHz/OS X 10.4.11
Compress Decompress
32-bit: -22.8 to -9.56% -26.0 to +3.76%
Relative performance to TigerVNC 1.0.0:
Compress Decompress
64-bit: 2.20 to 2.54x 2.11 to 2.54x
32-bit: No change +12.4 to +21.2%
In the aggregate, libjpeg/SIMD is now about an 80-90% solution relative
to IPP. 32-bit compression is still its weakness, particularly on Intel
chips. However, 64-bit performance and 32-bit decompression performance
on AMD chips is very strong and is often even faster than IPP. On older
64-bit AMD processors which lack SSE3, libjpeg/SIMD will be the clear
victor, since 64-bit IPP does not support SSE2 instructions.
Looking at just the 4:4:4 performance, which is the case most likely to
be used on a LAN (where these types of performance differences would be
the most obvious), the performance is generally toward the high side of
the ranges listed above, making libjpeg/SIMD a 90-95% solution in the
aggregate relative to IPP.
Since this codec is now also integrated with the evolving VirtualGL 2.2
code base, I will be maintaining it in both projects and will make
changes to it later on if I discover any obvious improvements, but for
now, I'm happy with shipping it the way it is, barring any unforeseen
breakage.
Darrell
tigervncvsipp3.ods
Description: Binary data
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