Intel confirms Alder Lake-P & H mobile specs, publishes hybrid architecture optimization guide for developers

Published: 15th Oct 2021, 14:57 GMT   Comments

Intel Alder Lake mobile confirmed up to 14 cores

Intel released a developer guide for its 12th Gen Core series. The document outlines the necessary steps to optimize software for hybrid architectures such as Alder Lake.

Alder Lake Mobile Specifications

Intel Alder Lake will feature two types of cores: Efficient (small) and Performance (big). Each type of core will have its purpose and they should not always be used for the same tasks. The company confirmed that the Alder Lake-P series, which will be replacing Tiger Lake-U, will offer up to 2 Performance cores and 8 Efficient cores (the A in the diagram refers to Atom core). At the same time, the next-gen H-series will feature 6 Performance cores and 8 Efficient cores.

Intel Alder Lake CPU configurations, Source: Intel

All those configurations have already been mentioned numerous times in the leaks. In fact, they were even shown in Intel’s own presentation at Architecture Day 2021. However, they were never officially attached to any specific sub-series, as they are in the new document.

Intel Alder Lake CPU types as shown at Architecture Day 2021, Source: Intel

Alder Lake with AVX512?

The guide claims that Intel Alder Lake CPUs will have AVX512 instructions but only when Efficient cores are disabled. It is up to OEMs to device whether AVX512 options should be available on the CPU:

However it has been quickly confirmed by Ian Cutress from Anandtech that this is in fact a mistake and the guide will soon be updates:

Alder Lake optimization scenarios

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.

“Golden Cove” (P-cores) and “Gracemont” (E-cores) feature separate L1 and L2 caches so they can run largely independently of each other. The L3 (LLC) cache is shared, Source: Intel

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.

Optimization scenarios for Intel Alder Lake, Source: Intel

Intel is also mentioning the gaming performance of the desktop Alder Lake-S series specifically. What stands out is Intel finally admitting that games may use more than six to eight cores:

[…] Games are a critical segment for Alder Lake-S (ADL-S), and no performance loss is acceptable. While many games are GPU-bound, top AAA titles operating on high-end discrete GPUs are often CPU-bound. The games will generally be CPU-bound on one or two critical threads, and they will feature a tasking system enumerated to either the logical or physical processor counts. As it is difficult to remove work from the critical game threads, Amdahl’s Law often prevents core-count scaling beyond six to eight cores, but this does not mean that games do not use more than six to eight threads/cores.

Alder Lake coming to all PC market segments

The documents also confirm that Alder Lake will launch for desktop, notebook, ultrabook, and 2-in-1 devices, while only mentioning the first launch scheduled for Q4 2021:

Will Alder Lake only be available on desktop PCs, or will it also be available in notebooks and other form-factors?
The Alder Lake platform will be available for desktop, notebook, Ultrabook, and convertible form-factors with various SKUs.

Associating caches with cores using GroupID/Mask, otherwise known as a group mask, Source: Intel

Intel 12th Gen Core series “Alder Lake” is to launch on November 4th, but the company is yet to make a formal announcement at its Innovation event on October 27th. The mobile SKUs mentioned in this guide are not expected to hit the market until the first quarter of next year.

Source: Intel via @Dellchannel21

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