linux-kernel - RE: [PATCH v2] mshv: Add support for integrated scheduler

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Message-ID:
 <SN6PR02MB41571179407BBD9F18267622D49FA@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Fri, 30 Jan 2026 01:29:27 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
	"kys@...rosoft.com" <kys@...rosoft.com>, "haiyangz@...rosoft.com"
	<haiyangz@...rosoft.com>, "wei.liu@...nel.org" <wei.liu@...nel.org>,
	"decui@...rosoft.com" <decui@...rosoft.com>, "longli@...rosoft.com"
	<longli@...rosoft.com>
CC: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] mshv: Add support for integrated scheduler

From: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com> 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 <anpintil@...rosoft.com>
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
> ---
>  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 <mhklinux@...look.com>