Kubernetes v1.34: Introducing CPU Manager Static Policy Option for Uncore Cache Alignment

Kubernetes v1.34: Introducing CPU Manager Static Policy Option for Uncore Cache Alignment Understanding the feature What is uncore cache? Cache-aware workload placement Use cases Enabling the feature Further reading Getting involved A new CPU Manager Static Policy Option called prefer-align-cpus-by-uncorecache was introduced in Kubernetes v1.32 as an alpha feature, and has graduated to beta in Kubernetes v1.34. This CPU Manager Policy Option is designed to optimize performance for specific workloads running on processors with a split uncore cache architecture. In this article, I'll explain what that means and why it's useful. prefer-align-cpus-by-uncorecache Until relatively recently, nearly all mainstream computer processors had a monolithic last-level-cache cache that was shared across every core in a multiple CPU package. This monolithic cache is also referred to as uncore cache (because it is not linked to a specific core), or as Level 3 cache. As well as the Level 3 cache, there is other cache, commonly called Level 1 and Level 2 cache, that is associated with a specific CPU core. In order to reduce access latency between the CPU cores and their cache, recent AMD64 and ARM architecture based processors have introduced a split uncore cache architecture, where the last-level-cache is divided into multiple physical caches, that are aligned to specific CPU groupings within the physical package. The shorter distances within the CPU package help to reduce latency. Kubernetes is able to place workloads in a way that accounts for the cache topology within the CPU package(s). The matrix below shows the CPU-to-CPU latency measured in nanoseconds (lower is better) when passing a packet between CPUs, via its cache coherence protocol on a processor that uses split uncore cache. In this example, the processor package consists of 2 uncore caches. Each uncore cache serves 8 CPU cores.