Cita:
... Why is the SMT scaling of Zen 5 so different? AMD didn't mention anything about SMT in their press briefings, other than the fact that it exists. If they made significant changes wouldn't they have told us about them? Is this a bug or a feature? Is AMD able to look at multithreaded scaling and make improvements? I'm quite sure that is the case, especially the gains for gaming performance are tempting. While those are somewhat game-specific, it shouldn't be too hard to come up with some logic to address this. In the briefings we heard some vague comments that AMD is using AI-trained networks inside the CPU to optimize operation, maybe that mechanism could be used for better thread placement? Just to clarify, there is no training while the CPU is running in your system, the network is generated during design-time in AMD's labs. However, I would expect that it is upgradeable through microcode somehow. In the past AMD has made changes to the behavior of their processors through AGESA BIOS updates, I think they will address the scheduling similarly.
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On the topic of Microsoft, the Windows operating system is executing the actual thread placement, the processor just hints at what it thinks is an optimal placement. Intel uses a hardware component called Thread Director for this, AMD uses a slightly different approach, but their BIOS does provide guidance to the OS, like for example the CPPC2 Preferred Cores mechanism. There are also a number of undocumented settings for Windows Power Plan, which could be another way to improve the scheduling.
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