Intel Software Defined Silicon planned for integration in Linux 5.18

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We still don’t know what features Intel plans to capitalize on with its Software Defined Silicon “SDSi” feature in future processors, but it turns out that the core core of necessary software support is now extended to land with Linux 5.18. With support for the SDSi kernel coming together quite quickly, it’s possible we’ll see Software Defined Silicon soon.

Last September, I was the first to draw attention to Intel’s patches for Software Defined Silicon to enable additional licensed hardware features on Linux. The kernel driver is about handling the necessary cryptographic activation of “additional silicon features”, but the framework is rather generic and does not specify to what extent Intel plans to now make processor features available as an upgrade. additional level/license.

After drawing attention to the fixes, the folks at The Register then went on to request Intel about SDSi. Intel responded by saying: “We won’t go into much detail about Software Defined Silicon just yet. As you know, Intel regularly submits code to the Linux kernel that could be used in future products. And that’s what happened in this case. If we plan to implement these updates in future products, we will provide a more in-depth explanation of how they are implemented at that time.

But since then, Intel has continued to work on SDSi Linux code with this new driver to enable additional CPU features. Now it turns out they are working to get Software Defined Silicon support into the next Linux kernel release.

Following v6 patches, Hans de Goede of Red Hat maintaining the x86 platform driver subsystem commented that he plans to review his pilot exam next week with plans to prepare him for mainlining: “Assuming no major issues are found, the plan is definitely to integrate it before the 5.18 merge window.

So it looks like SDSi is moving forward and unless some last minute issues are found in Linux 5.18. The v5.18 merge window kicks off at the end of March while the stable kernel will be here around the end of May.

Based on this fairly quick timing since patches were quickly overhauled in Q4 and now lined up for Linux 5.18, it’s possible that SDSi will debut for Xeon Scalable “Sapphire Rapids” or perhaps more likely the successor to the Rocket Lake Xeon W-1300 / E-2300 Series aka Alder Lake Xeon chips… There have been various rumors recently about Alder Lake Xeon chips and it would make more sense for Intel to use SDSi there with their chips server/workstation models rather than the high-end Xeon Scalable processors. Anyway, with some interest/emphasis on preparing SDSi for Linux 5.18, it’s probably to prepare for chips coming this year and not 2023~2024.

One possibility that comes to mind is Intel gating AVX-512 with Alder Lake Xeon chips as an SDSi upgrade feature. We know that Alder Lake P-cores have AVX-512 when E-cores are disabled and enable AVX-512 from the BIOS, but more recently motherboard vendors have started to remove this feature from their motherboards altogether. Alder Lake S consumer desktop motherboards. It will be interesting to see how AVX-512 handles with Alder Lake Xeon CPUs if this feature is enabled – or maybe that’s where Software Defined Silicon makes its debut. Placing AVX-512 behind SDSi would also potentially free up some software complexities related to the fact that AVX-512 is only available on P cores with hybrid CPU designs. As of my last check, the Linux kernel does not have the logic for task placement where AVX-512 execution can only occur from certain threads/cores/automatic migration when looking for an instruction not supported by the current kernel, however short it is wired, it would depend on the user/administrator (or a daemon) pinning the AVX-512 tasks to the P cores. If a user goes through the steps of SDSi activation (and running a sufficiently recent kernel) and paying extra to get AVX-512, the user/administrator is probably aware of these limitations and can then ensure that AVX-512 workloads will properly configure their software environment.

Anyway, in short, Intel Software Defined Silicon should land with Linux 5.18. Intel has yet to offer any public announcements or guidance on how they plan to market around SDSi, but it will be interesting to see…Although this is just speculation for now, given the current state of Alder Lake on the consumer side with AVX-512 actually being present for P cores, I can’t help but wonder if their next entry level Xeon chips might have AVX-512 for P cores as an opt-in/upgrade feature. We will see.

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