Hybrid vCPU: Tencent Cloud's Exploration of Virtualizing Heterogeneous CPU Architecture

This article introduces Tencent Cloud's technical exploration of Hybrid vCPU virtualization, presented at KVM Forum 2023. As cloud computing demands become increasingly diverse and complex with deeper customization requirements, hardware vendors have introduced heterogeneous computing architectures that balance power consumption and performance in client computing markets.

The content covers three development stages of Hybrid CPU architecture: Stage 1 features homogeneous instruction set architecture (ISA) with different microarchitectures (P-core and E-core); Stage 2 introduces ISA-level heterogeneity where different cores support different instruction sets; Stage 3 envisions co-existence of x86, ARM, and RISC-V cores on the same physical silicon.

The article details the motivation for implementing Hybrid vCPU in virtualization: enabling VMs to perceive real CPU topology information for better performance optimization, supporting online CPU feature control for live migration flexibility, enhancing security by dynamically removing vulnerable CPU features, and improving data center resource utilization by utilizing partially defective cores.

Key implementation aspects include: defining Hybrid vCPU virtualized space covering CPU topology, frequency, cache topology, and PMU features; applying Hybrid vCPU to connect multiple VM pools for seamless feature migration; implementing online vPMU feature control; and addressing challenges such as BSP initialization, per-CPU driver support, and hot-plug compatibility.