<https://software.intel.com/en-us/articles/google-vp9-optimization>
Intel describing how they improved the performance of the VP9 decoder for
Silvermont, a recent Atom core.
The meat is several not-really-obvious changes to the code to overcome
limitations of the instruction decoder. The optimizations seem particular
to Silvermont but the article says:
Testing against the future Intel Atom platforms, codenamed Goldmont and
Tremont, the VP9 optimizations delivered additional gains.
These optimizations did nothing for Core processors as far as I can tell.
I don't know if it affects any AMD processors.
A RISC processor would not have a complex instruction decoder so this kind
of hacking would not apply. I will admit that there are "hazards" in RISC
processors that are worth paying attention to when selecting and ordering
instructions but these tend to be clearer.
Another thing in the paper:
The overall results were outstanding. The team improved user-level
performance by up to 16 percent (6.2 frames per second) in 64-bit
mode and by about 12 percent (1.65 frames per second) in 32-bit
mode. This testing included evaluation of 32-bit and 64-bit GCC
and Intel® compilers, and concluded that the Intel compilers
delivered the best optimizations by far for Intel® Atom™
processors. When you multiply this improvement by millions of
viewers and thousands of videos, it is significant. The WebM team
at Google also recognized this performance gain as extremely
significant. Frank Gilligan, a Google engineering manager,
responded to the team’s success: “Awesome. It looks good. I can’t
wait to try everything out.” Testing against the future Intel Atom
platforms, codenamed Goldmont and Tremont, the VP9 optimizations
delivered additional gains.
Consider 64-bit. If 16% improvement is 6.2 f/s, then the remaining 84%
would be 32.55 f/s. Not great, but OK.
For 32-bit, 12% is 1.65 f/s; the remaining 88% would be 12 f/s. Totally
useless, I think.
Quite interesting how different these two are.---
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