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

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Message-ID: <20260204071816.GN79272@liuwe-devbox-debian-v2.local>
Date: Wed, 4 Feb 2026 07:18:16 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
	decui@...rosoft.com, longli@...rosoft.com,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] mshv: Add support for integrated scheduler

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@...rosoft.com>
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@...ux.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.

Wei

> +
>  	/* Resource properties */
>  	HV_PARTITION_PROPERTY_GPA_PAGE_ACCESS_TRACKING		= 0x00050005,
>  	HV_PARTITION_PROPERTY_UNIMPLEMENTED_MSR_ACTION		= 0x00050017,
> @@ -102,7 +105,7 @@ enum hv_partition_property_code {
>  };
>  
>  #define HV_PARTITION_VMM_CAPABILITIES_BANK_COUNT		1
> -#define HV_PARTITION_VMM_CAPABILITIES_RESERVED_BITFIELD_COUNT	59
> +#define HV_PARTITION_VMM_CAPABILITIES_RESERVED_BITFIELD_COUNT	57
>  
>  struct hv_partition_property_vmm_capabilities {
>  	u16 bank_count;
> @@ -119,6 +122,8 @@ struct hv_partition_property_vmm_capabilities {
>  			u64 reservedbit3: 1;
>  #endif
>  			u64 assignable_synthetic_proc_features: 1;
> +			u64 reservedbit5: 1;
> +			u64 vmm_enable_integrated_scheduler : 1;
>  			u64 reserved0: HV_PARTITION_VMM_CAPABILITIES_RESERVED_BITFIELD_COUNT;
>  		} __packed;
>  	};
> 
> 
>