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LigH · 10th October 2018, 23:40

Just a hint:

Code:

x265.exe --no-asm --version
x265 [info]: HEVC encoder version 2.9+1-169e76b6bbcc
x265 [info]: build info [Windows][GCC 8.2.0][64 bit] 8bit+10bit+12bit
x265 [info]: using cpu capabilities: none!

All assembler optimizations forbidden = only basic C/C++ code used.

But if all assembler optimizations are enabled (and all of them are usually linked in the encoder), it only means they are available in case your CPU supports them (which is detected at runtime). It doesn't mean all of them are used on every hardware. If you don't limit them with the --asm mask parameter, x265 detects what your CPU supports while starting, and selects the code paths with the optimal speed supported by your specific CPU.

Code:

x265.exe --version
x265 [info]: HEVC encoder version 2.9+1-169e76b6bbcc
x265 [info]: build info [Windows][GCC 8.2.0][64 bit] 8bit+10bit+12bit
x265 [info]: using cpu capabilities: MMX2 SSE2Fast LZCNT

This x265.exe contains code paths for time-critical assembler routines for MMX+SSE2, SSSE3+SSE4, AVX, and even AVX2. But it runs on an AMD Phenom-II, so it is limited to MMX+SSE2 by the CPU auto-detection.

The very same x265.exe can use AVX or even AVX2 code if you copy it onto a PC with a CPU that supports AVX or even AVX2 and run it there.

{EDIT}If your CPU even supports AVX512, and you insist in using AVX512 instructions, then you need to enable it with an additional parameter --asm avx512 in your command line because it is a bit risky and does not always provide better performance, especially not when your CPU gets temperature throttled. And it will crash if your CPU does not support AVX512.{/EDIT}

So what are these special executables provided on a few sites? In addition to multiple code paths for time-critical assembler routines, also non-critical C/C++ routines get optimized for a modern instruction set, which limits their compatibility; these builds will not even start on older CPU's.

If I would use an x265.exe which was built with C/C++ compiler optimizations for AVX (that is probably what you read for special binaries), it would crash right at the start if run on an AMD Athlon/Phenom which doesn't support AVX, because it would use AVX instructions already for the initialization, already before the encoding even starts. But this is not a time-critical part. There is no serious need to speed up code which runs only once or a few times. – (Jedi mind powers) "This is not the build you are looking for."

Rather generic builds, like mine or Barough's or Midzuki's, are fine for a large range of PC's; builds for x86-64 are probably optimized at least for SSE2 in the code generated by the C/C++ compiler, which is the minimal widely supported instruction set of AMD64 compatible CPU's. And the selection of highly optimized assembler routines for the really time-critical parts is done in the encoder at runtime.

10th October 2018, 23:40	#6407 \| Link
LigH German doom9/Gleitz SuMo Join Date: Oct 2001 Location: Germany, rural Altmark Posts: 6,782	Just a hint: Code: x265.exe --no-asm --version x265 [info]: HEVC encoder version 2.9+1-169e76b6bbcc x265 [info]: build info [Windows][GCC 8.2.0][64 bit] 8bit+10bit+12bit x265 [info]: using cpu capabilities: none! All assembler optimizations forbidden = only basic C/C++ code used. But if all assembler optimizations are enabled (and all of them are usually linked in the encoder), it only means they are available in case your CPU supports them (which is detected at runtime). It doesn't mean all of them are used on every hardware. If you don't limit them with the --asm mask parameter, x265 detects what your CPU supports while starting, and selects the code paths with the optimal speed supported by your specific CPU. Code: x265.exe --version x265 [info]: HEVC encoder version 2.9+1-169e76b6bbcc x265 [info]: build info [Windows][GCC 8.2.0][64 bit] 8bit+10bit+12bit x265 [info]: using cpu capabilities: MMX2 SSE2Fast LZCNT This x265.exe contains code paths for time-critical assembler routines for MMX+SSE2, SSSE3+SSE4, AVX, and even AVX2. But it runs on an AMD Phenom-II, so it is limited to MMX+SSE2 by the CPU auto-detection. The very same x265.exe can use AVX or even AVX2 code if you copy it onto a PC with a CPU that supports AVX or even AVX2 and run it there. {EDIT}If your CPU even supports AVX512, and you insist in using AVX512 instructions, then you need to enable it with an additional parameter --asm avx512 in your command line because it is a bit risky and does not always provide better performance, especially not when your CPU gets temperature throttled. And it will crash if your CPU does not support AVX512.{/EDIT} So what are these special executables provided on a few sites? In addition to multiple code paths for time-critical assembler routines, also non-critical C/C++ routines get optimized for a modern instruction set, which limits their compatibility; these builds will not even start on older CPU's. If I would use an x265.exe which was built with C/C++ compiler optimizations for AVX (that is probably what you read for special binaries), it would crash right at the start if run on an AMD Athlon/Phenom which doesn't support AVX, because it would use AVX instructions already for the initialization, already before the encoding even starts. But this is not a time-critical part. There is no serious need to speed up code which runs only once or a few times. – (Jedi mind powers) "This is not the build you are looking for." Rather generic builds, like mine or Barough's or Midzuki's, are fine for a large range of PC's; builds for x86-64 are probably optimized at least for SSE2 in the code generated by the C/C++ compiler, which is the minimal widely supported instruction set of AMD64 compatible CPU's. And the selection of highly optimized assembler routines for the really time-critical parts is done in the encoder at runtime. __________________ New German Gleitz board MediaFire: x264 \| x265 \| VPx \| AOM \| Xvid Last edited by LigH; 11th October 2018 at 08:17.