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Strange result in x265 test

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  • Strange result in x265 test

    My x265 result on a Ryzen 7 3700X system seems really out of whack. I get, quite consistently, 9.87 fps. Looking at the x265 results, it should be more like 51.4 fps. Under 10 fps would be a much slower processor.

    I'd expect performance on x264 would be very similar to x265. A Ryzen 7 3700X moves from 67th to 61th percentile, not much change. I get 98.48 fps in this test, slightly faster than expected value of 94 fps.

    Other tests, e.g. kernel compile, cachebench, ramspeed, etc., are pretty much as expected.

    So why would I get an extremely slow result just on x265? Seems like maybe there is something wrong with the test. Or is it possible for this test to use GPU acceleration and that is failing for some reason?

  • #2
    Guessing one of your yasm installation provided by the system is messed up and so for some reason x265 is falling back to its generic (slow) code. Though off hand I think x264 is also using yasm. But that would be my immediate guess is something odd with yasm/nasm on the systemm.
    Michael Larabel
    http://www.michaellarabel.com/

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    • #3
      I tried debug-install to see what's going on. Nothing stood out as a problem:
      Code:
      …
      -- Found nasm: /usr/bin/nasm (found version "2.14.02")  
      -- Found Nasm 2.14.02 to build assembly primitives
      -- x265 version 3.1.2+1-76650bab70f9
      -- The ASM_NASM compiler identification is NASM
      -- Found assembler: /usr/bin/nasm
      …
      [  7%] Building ASM_NASM object common/CMakeFiles/common.dir/x86/pixel-a.asm.o
      I supposed there could be a problem with x265 and gcc 10.2.1. Maybe there is a way to search the x265 results by compiler used?

      Or an issue with the test running the system x265 copy instead of PTS's copy, or the test's x265 binary being linked against the system libx265. Or course the FC32 x265 being incredibly slow and no one noticing is unlikely.

      Or maybe the encoding is not using the right x265 options? The very fast to the very slow preset is huge difference in speed. Easily enough the explain the difference.

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      • #4
        After rebuilding with debug-install, the fps is back to the expected value. It must not have built correctly the first time. I've not reinstalled nasm, so I don't know why that would have changed. Unfortunately, it doesn't seem like there's an old build log to check. I should have checked that before I rebuilt it.

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