6/3/2023 0 Comments Handbreak intel power gadget![]() ![]() All you have to do is adding a colon (without spaces) at the end, which separates the individual parameters, and adding “asm=avx512” after that. In HandBrake, this is done in the Video Encoder settings-you select x265 and at the bottom in the “Advanced Options” field, you can see extra command line parameters that are to be passed to x265. However, if you are using a GUI or frontend, you need to find out how to pass the parameter to x265. ![]() Use this if you are running x265.exe directly. Using the AVX-512 in x265 can be forced by using the commandline parameter ‑‑asm avx512. How to turn AVX-512 on (in x265 and Handbrake)? This should hopefully also be the case for Rocket Lake processors, which should keep their clock high on Z590 motherboards, even with AVX-512 engaged. However, if your processor is overclocked to a fixed rate or for some other reason the AVX-512 does not reduce its clock speed, you should generally notice a performance boost. The developers have recommended turning on the AVX-512 when, for example, you are encoding 4K with very slow settings. And this setting seems to have stayed the same since then. And that’s why a decision was made to leave this code disabled by default- hence x265 won’t use it until you force it on (you can read about it here). In other words, the combined result was slowdown instead of speedup. When the x265 initially received the assembly optimizations making use of AVX-512, it was discovered that they did not increase performance on the Xeon processors by the same or better factor as they caused the clock speed to decrease. Therefore, Xeon processors have to reduce clock rates when using these instructions, which has an impact on the performance boost that is realised. Crucially, AVX-512 doesn’t just process twice the data in one instruction, it also increases power consumption of the CPU core. Why doesn’t the x265 encoder use AVX-512 by default? This is because these optimizations cover only some of the encoder operations, and as a result the encoding FPS boost is relatively low-don’t expect anything close to the 100% speedup that a 2x wider SIMD vector could achieve in isolated operations, in theory. On Rocket Lake, it should look like this by default: x265 : using cpu capabilities: MMX2 SSE2Fast LZCNT SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2 You can check that this is true in the log, which reports “using cpu capabilities” line with a list of instruction extensions that the program actually employs during encoding. The program only uses AVX2 (as well as some other instruction sets like BMI2, AVX and of course different versions of SSE). So when you just launch HandBrake or the commandline x265 executable, they won’t use the builtin AVX-512 support and Rocket Lake processors won’t benefit from the instructions either. These tests suffer from one problem when it comes to AVX-512 enabled processors however, and that is that ever since optimizations using AVX-512 instructions were added to x265 (back in 2018), the program has kept them disabled by default. We already provide x265 encoding benchmarks of Rocket Lake processors that are included in our CPU testing, in which we test in HandBrake with default settings, as lots of other websites do. We’ll show you how to turn it on and what are the effects. It’s little known, but x265 does not actually use AVX-512 by default. ![]() We looked at one use: encoding HEVC video via x265. One area where AVX-512 promises better performance is multimedia. The 11th generation Intel Core processors (Rocket Lake) are the first mainstream desktop parts supporting AVX-512 instruction set, previously only available in Xeons or the X299 platform. ![]() AVX-512 for x265: how to use it, the effects on performance and the price you pay in power consumption ![]()
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