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Today Xen is scheduling guest virtual cpus on all available physical cpus independently from each other. Recent security issues on modern processors (e.g. L1TF) require to turn off hyperthreading for best security in order to avoid leaking information from one hyperthread to the other. One way to avoid having to turn off hyperthreading is to only ever schedule virtual cpus of the same guest on one physical core at the same time. This is called core scheduling.
This presentation shows results from the effort to implement core scheduling in the Xen hypervisor. The basic modifications in Xen are presented and performance numbers with core scheduling active are shown.