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takyon writes:

Intel published a developer guide confirming details of its upcoming Alder Lake processors.

Desktop "Alder Lake-S" processors will include up to 8 "Golden Cove" performance cores (P-cores), 8 "Gracemont" (Atom) efficiency cores (E-cores), and 32 graphics execution units (Gen 12.2 EUs). A smaller die will include only up to 6 P-cores and no E-cores, to be used in lower-end products such as a 6-core Intel Core i5-12400 or a quad-core i3.

Mobile "Alder Lake-P" processors will include up to 6 P-cores, 8 E-cores, and 96 graphics EUs. A smaller "ultra mobile" die will include up to 2 P-cores and 8 E-cores.

AVX-512 is physically present on Golden Cove cores, but disabled in Alder Lake.

The guide mainly focuses on software implementations for hybrid CPUs. It provides various optimization strategies for Alder Lake, including lack of optimization, a "Good Scenario", and the "Best Scenario". According to the document, lack of optimization will not mean that the CPU will be unable to distribute workloads for hybrid CPUs, which should be handled by ThreadDirector anyway, but some may be distributed to the wrong types of cores, should the scheduling algorithm not recognize the task.

In the "Good Scenario," Intel assumes that the application will be aware of the hybrid architecture. The primary tasks should target Performance cores, whereas non-essential and background threads with lower priority should target Effcieent cores.

The "Best Scenario" goes into further detail about which workloads specifically should target Efficient cores: Shader Compilation, Audio Mixing, Asset Streaming, Decompression, Any other non-critical work.

Intel's Thread Director combines a microcontroller with software-based scheduling:

Intel's Thread Director controller puts an embedded microcontroller inside the processor such that it can monitor what each thread is doing and what it needs out of its performance metrics. It will look at the ratio of loads, stores, branches, average memory access times, patterns, and types of instructions. It then provides suggested hints back to the Windows 11 OS scheduler about what the thread is doing, whether it is important or not, and it is up to the OS scheduler to combine that with other information about the system as to where that thread should go. Ultimately the OS is both topologically aware and now workload aware to a much higher degree.

Inside the microcontroller as part of Thread Director, it monitors which instructions are power hungry, such as AVX-VNNI (for machine learning) or other AVX2 commands that often draw high power, and put a big flag on those for the OS for prioritization. It also looks at other threads in the system and if a thread needs to be demoted, either due to not having enough free P-cores or for power/thermal reasons, it will give hints to the OS as to which thread is best to move. Intel states that it can profile a thread in as little as 30 microseconds, whereas a traditional OS scheduler may take 100s of milliseconds to make the same conclusion (or the wrong one).

On top of this, Intel says that Thread Director can also optimize for frequency. If a thread is limited in a way other than frequency, it can detect this and reduce frequency, voltage, and power. This will help the mobile processors, and when asked Intel stated that it can change frequency now in microseconds rather than milliseconds.

[...] On the question of Linux, Intel only went as far to say that Windows 11 was the priority, and they're working upstreaming a variety of features in the Linux kernel but it will take time. An Intel spokesperson said more details closer to product launch, however these things will take a while, perhaps months and years, to get to a state that could be feature-parity equivalent with Windows 11.

See also: Intel 12th gen Alder Lake-P and Alder Lake-M mobile SKUs to enter production between Q4 2021 and Q1 2022; Up to 14 cores, Xe GT3, PCie Gen5, and DDR5 on the anvil
Linux 5.16 To Add Intel Encrypted PXP, Alder Lake S Declared Stable & Ready
Alder Lake Support Added To Intel's TCC Driver In Linux 5.15
Scheduler Changes For Linux 5.15 - Still No Sign Of Any Intel Thread Director Optimizations

Previously: Windows 11 Bashes Some AMD Procs; Boosts Some Intel Core i7 Alder Lake

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