Intel's mysterious Software Defined Silicon (SDSi) mechanism for adding features to Xeon CPUs will be officially supported in Linux 5.18, the next major release of the operating system. SDSi allows users to add features to their CPU after they've already purchased it. Formal SDSi support means that the technology is coming to Intel's Xeon processors that will be released rather shortly, implying Sapphire Rapids will be the first CPUs with SDSi.
Intel started to roll out Linux patches to enable its SDSi functionality in the OS last September. By now, several sets of patches have been released and it looks like they will be added to Linux 5.18, which is due this Spring. Hans de Goede, a long-time Linux developer who works at Red Hat on a wide array of hardware enablement related projects, claims that SDSi will land in Linux 5.18 if no problems emerge, reports Phoronix.
"Assuming no major issues are found, the plan definitely is to get this in before the 5.18 merge window," said de Goede.
Intel Software Defined Silicon (SDSi) is a mechanism for activating additional silicon features in already produced and deployed server CPUs using the software. While formal support for the functionality is coming to Linux 5.18 and is set to be available this spring, Intel hasn't disclosed what exactly it plans to enable using its pay-as-you-go CPU upgrade model. We don't know how it works and what it enables, but we can make some educated guesses.
Every generation of Intel Xeon CPUs adds multiple capabilities to make Intel's server platform more versatile. For example, in addition to microarchitectural improvements and new instructions, Intel's Xeon Scalable CPUs (of various generations) added support for up to 4.5TB of memory per socket, network function virtualization, Speed Select technology, and large SGX enclave size, just to name a few. In addition, there are optimized models for search, virtual machine density, infrastructure as a service (IaaS), software as a service (SaaS), liquid cooling, media processing, and so on. With its 4th Generation Xeon Scalable 'Sapphire Rapids' CPUs, Intel plans to add even more features specialized for particular use cases. You can see an example of the SKU stack above, and it includes all types of different Xeon models:
- L- Large DDR Memory Support (up to 4.5TB)
- M- Medium DDR Memory Support (up to 2TB)
- N- Networking/Network Function Virtualization
- S- Search
- T- Thermal
- V- VM Density Value
- Y- Intel Speed Select Technology
But virtually none of Intel's customers need all the supported features, which is why Intel has to offer specialized models. There are 57 SKUs in the Xeon Scalable 3rd-Gen lineup, for example. But from a silicon point of view, all of Intel's Xeon Scalable CPUs are essentially the same in terms of the number of cores and clocks/TDP, with various functionalities merely disabled to create different models.
Intel certainly earns premium by offering workload optimized SKUs, but disabling certain features from certain models, then marking them appropriately and shipping them separately from other SKUs (shipped to the same client) is expensive — it can be tens of millions of dollars per year (or even more) of added logistical costs, not to mention the confusion added to the expansive product stack.
But what if Intel only offers base models of its Xeon Scalable CPUs and then allows customers to buy the extra features they need and enable them by using a software update? This is what SDSi enables Intel to do. Other use cases include literal upgrades of certain features as they become needed and/or repurposing existing machines. For example, if a data center needs to reconfigure CPUs in terms of clocks and TDPs, it would be able to buy that capability without changing servers or CPUs.
Intel yet has to disclose all the peculiarities of SDSi and its exact plans about the mechanism, but at this point, we are pretty certain that the technology will show up soon.
