The Road to Optimal CPU Virtualization on Hybrid Platform
Intel client platforms from Alderlake have begun to leverage hybrid CPU architectures, and hybrid CPU architectures can achieve a good balance of performance and power on bare metal. However, VMs are still unable to take advantage of the hybrid CPU architecture, not only because QEMU/KVM is unable to expose the P-core/E-core difference for VMs, but also because the P-core/E-core feature difference further blocks hybrid support in Guest. As a result, VM performance on hybrid platforms is very gapped from bare metal, and CPU features are not fully supported in Guest (e.g. PMU, which is disabled by KVM on hybrid platforms).
To address this, our presentation will mainly have the following aspects:
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Illustrate our proposal on how to design the QEMU API to allow users to create a hybrid CPU/cache topology for Guest, with flexible CPU type configurations. This allows Guest to realize the difference between the P-core/E-core type of the vCPU and different cache topologies. We achieve this by abstracting the topology device in QOM way to refactor current QEMU general topology implementation. We will also specifically describe our QOM-topology implementation and how it would help QEMU to improve the general topology subsystem.
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Present of our exploratory experience on VM performance optimization method could be applied for the VM with hybrid vCPUs. On Intel client platforms, there's ITD/ITMT, etc., which could optimize workload in VM based on hybrid CPU/cache topology.
In summary, this presentation will cover all aspects of reaching optimal CPU virtualization on hybrid platform for both performance and features.