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Definitely curious how this plays out: > Unfortunately, however, because Windows sees all of the cores as identical, it also has no proper insight into energy
by neogodless 3y ago
Definitely curious how this plays out:
> Unfortunately, however, because Windows sees all of the cores as identical, it also has no proper insight into energy efficiency here. Specifically, Windows has no idea that the Zen 4c cores are meant to be more energy efficient, so it will be making scheduling decisions based solely on workload/frequency metrics. This means that AMD is not able to take full advantage of the energy efficiency advantages offered by the Zen 4c CPU cores, as Windows isn't able to explicitly schedule threads on the more efficient cores. (An issue Intel gets around with their more meddlesome Thread Director)
Given that they are on feature parity with Zen 4, but trade higher clock speeds for density and efficiency - will we see the efficiency if Windows doesn't know any better?
Would Linux be able to do any better if it can tell the cores apart?
- tremon 3y agoYes, Linux is aware of asymmetric cores and can schedule more efficiently. big.LITTLE core architectures are more common in ARM systems, so Linux developed that support over ten years ago: https://lwn.net/Articles/501501/ https://lwn.net/Articles/501501/ The official documentation is at https://www.kernel.org/doc/html/latest/scheduler/sched-energy.html https://www.kernel.org/doc/html/latest/scheduler/sched-energ... . I don't know if the kernel already has an energy model that can apply to the Zen4/Zen4c cores, probably the model/instrumention must be explicitly added.
- Aardwolf 3y agoHow is Linux aware of this, are there CPU id instructions to differentiate the Zen4 from the Zen4c cores? If yes, is there any reason Windows can't receive a patch to be able to do so?
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- smoldesu 3y agoI am not an expert, but I believe it still requires some manufacturer effort on Linux. I bought an Alder Lake system pretty close to launch, and I had to wait a few months for kernel-side Thread Director[0] to fix asymmetric scheduling. Performance was really janky before that update, even though the power consumption and iGPU seemed fine. Nowadays things are fine, though I'm not sure how much of the asymmetric support was already in the kernel. > is there any reason Windows can't receive a patch to be able to do so? Probably not, given that Thread Director also runs on Windows AFAIK. AMD could probably cook up a solution if they needed one, but their E cores look pretty powerful from the get-go. My guess is that it won't need such a huge patch to perform well. [0] https://www.tomshardware.com/news/intel-thread-director-coming-to-linux-5-18 https://www.tomshardware.com/news/intel-thread-director-comi...
- adam_arthur 3y agoThis doesn't seem correct? "Windows 11 boosts performance of big.little x86 CPUs shows testing" https://www.neowin.net/news/windows-11-boosts-performance-of-biglittle-x86-cpus-shows-testing/ https://www.neowin.net/news/windows-11-boosts-performance-of... "Microsoft and Intel confirm Windows 11 is optimized for Big.Little design" https://www.neowin.net/news/microsoft-and-intel-confirm-windows-11-is-optimized-for-alder-lakes-biglittle-design/ https://www.neowin.net/news/microsoft-and-intel-confirm-wind...
- Dalewyn 3y agoWindows 11 knows how to use Intel performance and efficiency cores thanks to Intel providing Intel Thread Director which gives some hints to Windows 11's scheduler. AMD, from what I can tell, doesn't provide an equivalent to Intel Thread Director so Windows 11's scheduler has to work blind not unlike Windows 10's scheduler when working with Intel performance and efficiency cores. So all else being equal, it's reasonable to assume Windows 11 will not take full advantage of AMD's performance and efficiency core architecture because the scheduler is working blind.
- The_Colonel 3y ago> AMD, from what I can tell, doesn't provide an equivalent to Intel Thread Director Isn't that simply because AMD so far didn't have any heterogenous cores and they will quite possibly/likely work with Windows to add support for them (just like Intel did)? It might take some time, but it seems needlessly pessimistic to expect that this won't happen in some form.
- Sakos 3y agoBut why should it be on AMD? This needs to be a part of the OS as it is like in Linux, or as a user you're penalized for picking the company with less solid connections to Microsoft and less budget available to do something like Intel's thread director (which is how Intel's mixed cores are "supported" by Windows). Windows doesn't have any native support for heterogenous cores. It just takes the CPU's advice on what to do. That seems crazy to me.
- Sakos 3y agoI'm surprised that after 3 years since Intel's first big/little CPU (Lakefield), Windows still doesn't really support mixed cores. And that's over 10 years after the first ARM CPU with that kind of configuration. With their repeated attempts to get into the mobile space, you'd think they would've put more of an effort into this.
- torginus 3y agoThat simply seems untrue. Heterogeneous cores have existed since forever. SMT-aware has been a CPU feature in Windows for close to 2 decades, not to mention support for Intel's big-little designs
- tedunangst 3y agoHow much does it matter? The lines in the graph are pretty close together, and I'm assuming they picked an example that accentuates the difference.