From: Stanislav Kinsburskii <[email protected]> Sent: Thursday, January 29, 2026 12:08 PM > > Microsoft Hypervisor originally provided two schedulers: root and core. The > root scheduler allows the root partition to schedule guest vCPUs across > physical cores, supporting both time slicing and CPU affinity (e.g., via > cgroups). In contrast, the core scheduler delegates vCPU-to-physical-core > scheduling entirely to the hypervisor. > > Direct virtualization introduces a new privileged guest partition type - L1 > Virtual Host (L1VH) — which can create child partitions from its own > resources. These child partitions are effectively siblings, scheduled by > the hypervisor's core scheduler. This prevents the L1VH parent from setting > affinity or time slicing for its own processes or guest VPs. While cgroups, > CFS, and cpuset controllers can still be used, their effectiveness is > unpredictable, as the core scheduler swaps vCPUs according to its own logic > (typically round-robin across all allocated physical CPUs). As a result, > the system may appear to "steal" time from the L1VH and its children. > > To address this, Microsoft Hypervisor introduces the integrated scheduler. > This allows an L1VH partition to schedule its own vCPUs and those of its > guests across its "physical" cores, effectively emulating root scheduler > behavior within the L1VH, while retaining core scheduler behavior for the > rest of the system. > > The integrated scheduler is controlled by the root partition and gated by > the vmm_enable_integrated_scheduler capability bit. If set, the hypervisor > supports the integrated scheduler. The L1VH partition must then check if it > is enabled by querying the corresponding extended partition property. If > this property is true, the L1VH partition must use the root scheduler > logic; otherwise, it must use the core scheduler. This requirement makes > reading VMM capabilities in L1VH partition a requirement too. > > Signed-off-by: Andreea Pintilie <[email protected]> > Signed-off-by: Stanislav Kinsburskii <[email protected]> > --- > drivers/hv/mshv_root_main.c | 85 > +++++++++++++++++++++++++++---------------- > include/hyperv/hvhdk_mini.h | 7 +++- > 2 files changed, 59 insertions(+), 33 deletions(-) >
Looks good. Reviewed-by: Michael Kelley <[email protected]>
