Re: [RFC PATCH v2 0/5] Paravirt Scheduling (Dynamic vcpu priority management)

[Vineeth Remanan Pillai]

Sorry I missed sched_ext folks, adding them as well.

Thanks,
Vineeth


On Wed, Apr 3, 2024 at 10:01 AM Vineeth Pillai (Google)
<vineeth@xxxxxxxxxxxxxxx> wrote:
>
> Double scheduling is a concern with virtualization hosts where the host
> schedules vcpus without knowing whats run by the vcpu and guest schedules
> tasks without knowing where the vcpu is physically running. This causes
> issues related to latencies, power consumption, resource utilization
> etc. An ideal solution would be to have a cooperative scheduling
> framework where the guest and host shares scheduling related information
> and makes an educated scheduling decision to optimally handle the
> workloads. As a first step, we are taking a stab at reducing latencies
> for latency sensitive workloads in the guest.
>
> v1 RFC[1] was posted in December 2023. The main disagreement was in the
> implementation where the patch was making scheduling policy decisions
> in kvm and kvm is not the right place to do it. The suggestion was to
> move the polcy decisions outside of kvm and let kvm only handle the
> notifications needed to make the policy decisions. This patch series is
> an iterative step towards implementing the feature as a layered
> design where the policy could be implemented outside of kvm as a
> kernel built-in, a kernel module or a bpf program.
>
> This design comprises mainly of 4 components:
>
> - pvsched driver: Implements the scheduling policies. Register with
>     host with a set of callbacks that hypervisor(kvm) can use to notify
>     vcpu events that the driver is interested in. The callback will be
>     passed in the address of shared memory so that the driver can get
>     scheduling information shared by the guest and also update the
>     scheduling policies set by the driver.
> - kvm component: Selects the pvsched driver for a guest and notifies
>     the driver via callbacks for events that the driver is interested
>     in. Also interface with the guest in retreiving the shared memory
>     region for sharing the scheduling information.
> - host kernel component: Implements the APIs for:
>     - pvsched driver for register/unregister to the host kernel, and
>     - hypervisor for assingning/unassigning driver for guests.
> - guest component: Implements a framework for sharing the scheduling
>     information with the pvsched driver through kvm.
>
> There is another component that we refer to as pvsched protocol. This
> defines the details about shared memory layout, information sharing and
> sheduling policy decisions. The protocol need not be part of the kernel
> and can be defined separately based on the use case and requirements.
> Both guest and the selected pvsched driver need to match the protocol
> for the feature to work. Protocol shall be identified by a name and a
> possible versioning scheme. Guest will advertise the protocol and then
> the hypervisor can assign the driver implementing the protocol if it is
> registered in the host kernel.
>
> This patch series only implements the first 3 components. Guest side
> implementation and the protocol framework shall come as a separate
> series once we finalize rest of the design.
>
> This series also implements a sample bpf program and a kernel-builtin
> pvsched drivers. They do not do any real stuff now, but just skeletons
> to demonstrate the feature.
>
> Rebased on 6.8.2.
>
> [1]: https://lwn.net/Articles/955145/
>
> Vineeth Pillai (Google) (5):
>   pvsched: paravirt scheduling framework
>   kvm: Implement the paravirt sched framework for kvm
>   kvm: interface for managing pvsched driver for guest VMs
>   pvsched: bpf support for pvsched
>   selftests/bpf: sample implementation of a bpf pvsched driver.
>
>  Kconfig                                       |   2 +
>  arch/x86/kvm/Kconfig                          |  13 +
>  arch/x86/kvm/x86.c                            |   3 +
>  include/linux/kvm_host.h                      |  32 +++
>  include/linux/pvsched.h                       | 102 +++++++
>  include/uapi/linux/kvm.h                      |   6 +
>  kernel/bpf/bpf_struct_ops_types.h             |   4 +
>  kernel/sysctl.c                               |  27 ++
>  .../testing/selftests/bpf/progs/bpf_pvsched.c |  37 +++
>  virt/Makefile                                 |   2 +-
>  virt/kvm/kvm_main.c                           | 265 ++++++++++++++++++
>  virt/pvsched/Kconfig                          |  12 +
>  virt/pvsched/Makefile                         |   2 +
>  virt/pvsched/pvsched.c                        | 215 ++++++++++++++
>  virt/pvsched/pvsched_bpf.c                    | 141 ++++++++++
>  15 files changed, 862 insertions(+), 1 deletion(-)
>  create mode 100644 include/linux/pvsched.h
>  create mode 100644 tools/testing/selftests/bpf/progs/bpf_pvsched.c
>  create mode 100644 virt/pvsched/Kconfig
>  create mode 100644 virt/pvsched/Makefile
>  create mode 100644 virt/pvsched/pvsched.c
>  create mode 100644 virt/pvsched/pvsched_bpf.c
>
> --
> 2.40.1
>