Re: [PATCH v4] mshv: Add support for integrated scheduler

[Wei Liu <wei.liu@kernel.org>]

On Wed, Feb 04, 2026 at 07:18:16AM +0000, Wei Liu wrote:
> On Mon, Feb 02, 2026 at 07:26:06PM +0000, Stanislav Kinsburskii wrote:
> > Query the hypervisor for integrated scheduler support and use it if
> > configured.
> > 
> > Microsoft Hypervisor originally provided two schedulers: root and core. The
> 
> Microsoft Hypervisor provides three schedulers: root, classic
> (with or without SMT) and core. The latter two are hypervisor based.
> 
> > 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
> 
> Level-1 Virtualization Host.
> 
> > 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 <anpintil@microsoft.com>
> > Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> > ---
> [...]
> > +++ b/include/hyperv/hvhdk_mini.h
> > @@ -87,6 +87,9 @@ enum hv_partition_property_code {
> >  	HV_PARTITION_PROPERTY_PRIVILEGE_FLAGS			= 0x00010000,
> >  	HV_PARTITION_PROPERTY_SYNTHETIC_PROC_FEATURES		= 0x00010001,
> >  
> > +	/* Integrated scheduling properties */
> > +	HV_PARTITION_PROPERTY_INTEGRATED_SCHEDULER_ENABLED	= 0x00020005,
> 
> The internal name is "HvPartitionPropertyHierarchicalIntegratedSchedulerEnabled".
> 
> You missed the "Hierarchical" part in the property code name.
> 

I attempt to apply this patch and fix these issues. Unfortunately it
doesn't apply cleanly to hyperv-next.

Wei