Intel Cascade Lake Side Channel Mitigations
As an organization, Intel has inertia. Inertia in the form of always adding cores and features in new generations. In this generation, since Intel is not adding cores, what it is doing is mitigating impacts.
Note, the original version of this slide you may have seen online did not have L1TF. I asked Akhilesh about L1TF during Hot Chips and at some point, it made it into his presentation. That may have been due to the timing of the disclosure and initial presentation submission dates. L1TF is a major impact if an organization needs to turn off Hyper Threading as we covered in Intel Publishes L1TF and Foreshadow Performance Impacts and Foreshadow Flaw Targets Intel SGX and Virtual Machines. It is good to see that it is receiving a hardware mitigation along with Variant 2/3. Still, this means Cascade Lake is not the generation that Intel completely solves a next-generation branch prediction feature.
Like a Phoenix, Intel VNNI Reborn
Cascade Lake-SP VNNI is the new instruction. We first saw VNNI with Intel Xeon Phi Knights Mill for Machine Learning, an HPC chip that was canceled as the mainstream Xeon CPUs gained instructions of the former HPC parts.
Here is the INT16 version of VNNI:
Here is the INT8 version. Like traditional FMA, this is another instruction that allows fewer clock cycles per operation and therefore more performance.
We asked about performance. We expect VNNI to operate alongside AVX-512 clock curves. We also expect AVX-512 floating point and VNNI execution to be different than Knights Landing/ Mill insofar as a customer will have access to performant versions of both instructions.
Intel highlighted that for INT8 and INT16 operations, VNNI will greatly accelerate performance. This, combined with Intel’s investment in software, Intel hopes to provide a simple value proposition: you do not need a low power GPU. If you are going to install Cascade Lake CPUs, you can use VNNI for inferencing and do “fast enough” inferencing without adding different hardware.
Cascade Lake-SP’s Big Feature Optane Persistent Memory Support
The most anticipated feature of Cascade Lake-SP is support for Intel Optane DC Persistent Memory. Optane Persistent Memory puts Optane in a DDR4 DIMM package and allows high capacity persistent memory directly attached to DDR4 controllers instead of through the PCIe bus.
Much of the Hot Chips 30 presentation was focused on information we have already covered in Intel Optane DC Persistent Memory Sampling Today Revenue Delivery 2018 and Intel Data-Centric Innovation Summit Cascade Lake Optane and More. Check those for a refresher.
The actual hardware interface is DDR4 electrical and physical. Intel confirmed capacity details we published in our earlier piece Next-Gen Intel Cascade Lake 28C Supporting 3.84TB Memory.
The company also focused on the persistence domain. This is important because the software needs to know when data becomes persistent much like an acknowledge in traditional disk/ SSD storage.
If you are a software developer, get a Cascade Lake box with Optane Persistent Memory as soon as possible. The ability to integrate OPM is the killer tech of this generation.