Intel Architecture Day 2021 & The Linux State

Written by Michael Larabel in Processors on 19 August 2021. Page 2 of 6. 25 Comments

While Intel's Efficient Core is optimized for power and density efficient throughput, there is also the "Performance Core" known as Golden Cove. Intel's Performance x86 Core is designed to be scalable from laptops and desktops with Alder Lake through data centers with Xoen Sapphire Rapids. The Performance Core is wider, deeper, and designed to be smarter than previous microarchitectures. There is a new Fast Adder (FADD), AVX-512 FP16 support, and other new additions. It's great seeing AVX-512 FP16 for the Performance cores with Alder Lake -- Intel has been preparing the AVX-512 FP16 support for GCC and Clang though due to that timing won't be found in released versions of these compilers until late Q1 / early Q2 of next year.

There is a new power management controller with the Performance Core and will be interesting to see how well that works under Linux. So far I don't believe I've seen any new Linux kernel patches really changing things much for Alder Lake besides adapting the P-State CPUFreq driver to the notion of hybrid processor cores but at least no big power management changes from the kernel side.

At least under Windows, Intel is reporting their general-purpose performance with the Performance core to be around 19% higher overall than 11th Gen Intel Core performance.

On the data center side, one of the exciting aspects we've been looking forward to is Intel Advanced Matrix Extensions (AMX).

For the past year I have already been writing a lot about the Linux bring-up around AMX. It's still an ongoing process both for the Linux kernel AMX support as well as in user-space with the compiler toolchains -- hopefully all of it will get squared away in the coming months, but basically looking at early next year / spring 2022 Linux distributions for having the AMX support ready out-of-the-box.

One of the new areas covered around Alder Lake at Intel Architecture Day was Intel Thread Director. Intel Thread Director is their new hardware-based scheduler designed to be software transparent, real-time adaptive, and scalable from mobile to desktop. It's Intel Thread Director that will be responsible for placing tasks between the Power and Efficient cores on Alder Lake as well as handling any instruction capability differences. The slides note it's software transparent, which is good since I haven't seen any Linux kernel patches explicitly making mention of Thread Director. However, some of Intel's press materials also note that Windows 11 is optimized for Thread Director... So we'll see how well Linux does with Intel Thread Director and if any optimizations/improvements are necessary for the kernel.

Intel did confirm Alder Lake as having up to sixteen cores between the Performance and Efficient cores, up to 24 threads (the Efficient cores lack Hyper Threading), and up to a 30MB cache. Alder Lake is also confirmed for having DDR5-4800 and LP5-5200 support. On the connectivity front, PCI Express Gen 5 x16 capabilities are confirmed.

For Alder Lake availability, Intel is still citing that it will start in "Fall 2021." As covered across dozens of Phoronix articles, Intel has been bringing up Alder Lake on Linux for a while now. With the very latest Linux 5.13~5.14 state it looks like Alder Lake should be largely settled now aside from any possibly missing device IDs at the moment. Assuming no Linux issues around the new power management controller or Thread Director, I'm optimistic that it will be smooth sailing for Alder Lake on fall 2021 Linux distributions like Fedora 35 and Ubuntu 21.10. But, of course, stay tuned for Alder Lake Linux testing and benchmarking in due course to see how it all pands out on production hardware.

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