Re: [PATCH v2 0/4] hw/arm/virt: Support dirty ring

[Peter Maydell <peter.maydell@linaro.org>]

On Mon, 13 Mar 2023 at 07:13, Gavin Shan <gshan@redhat.com> wrote:
>
> On 2/27/23 12:26 PM, Gavin Shan wrote:
> > This series intends to support dirty ring for live migration for arm64. The
> > dirty ring use discrete buffer to track dirty pages. For arm64, the speciality
> > is to use backup bitmap to track dirty pages when there is no-running-vcpu
> > context. It's known that the backup bitmap needs to be synchronized when
> > KVM device "kvm-arm-gicv3" or "arm-its-kvm" has been enabled. The backup
> > bitmap is collected in the last stage of migration. The policy here is to
> > always enable the backup bitmap extension. The overhead to synchronize the
> > backup bitmap in the last stage of migration, when those two devices aren't
> > used, is introduced. However, the overhead should be very small and acceptable.
> > The benefit is to support future cases where those two devices are used without
> > modifying the code.
> >
> > PATCH[1] add migration last stage indicator
> > PATCH[2] synchronize the backup bitmap in the last stage of migration
> > PATCH[3] add helper kvm_dirty_ring_init() to enable dirty ring
> > PATCH[4] enable dirty ring for arm64
> >
> >     v1: https://lists.nongnu.org/archive/html/qemu-arm/2023-02/msg00434.html
> > RFCv1: https://lists.nongnu.org/archive/html/qemu-arm/2023-02/msg00171.html
> >
> > Testing
> > =======
> > (1) kvm-unit-tests/its-pending-migration and kvm-unit-tests/its-migration with
> >      dirty ring or normal dirty page tracking mechanism. All test cases passed.
> >
> >      QEMU=./qemu.main/build/qemu-system-aarch64 ACCEL=kvm \
> >      ./its-pending-migration
> >
> >      QEMU=./qemu.main/build/qemu-system-aarch64 ACCEL=kvm \
> >      ./its-migration
> >
> >      QEMU=./qemu.main/build/qemu-system-aarch64 ACCEL=kvm,dirty-ring-size=65536 \
> >      ./its-pending-migration
> >
> >      QEMU=./qemu.main/build/qemu-system-aarch64 ACCEL=kvm,dirty-ring-size=65536 \
> >      ./its-migration
> >
> > (2) Combinations of migration, post-copy migration, e1000e and virtio-net
> >      devices. All test cases passed.
> >
> >      -netdev tap,id=net0,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown  \
> >      -device e1000e,bus=pcie.5,netdev=net0,mac=52:54:00:f1:26:a0
> >
> >      -netdev tap,id=vnet0,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown \
> >      -device virtio-net-pci,bus=pcie.6,netdev=vnet0,mac=52:54:00:f1:26:b0
> >
> > Changelog
> > =========
> > v2:
> >    * Drop PATCH[v1 1/6] to synchronize linux-headers                            (Gavin)
> >    * More restrictive comments about struct MemoryListener::log_sync_global     (PeterX)
> >    * Always enable the backup bitmap extension                                  (PeterM)
> > v1:
> >    * Combine two patches into one PATCH[v1 2/6] for the last stage indicator    (PeterX)
> >    * Drop the secondary bitmap and use the original one directly                (Juan)
> >    * Avoid "goto out" in helper kvm_dirty_ring_init()                           (Juan)
> >
>
> Ping, Paolo and Peter Maydell. Please take a look to see if it can be
> merged, thanks!

No objections here; I'm assuming that since it's only touching
KVM core code that it would go via Paolo. However, as a new
feature it has missed softfreeze for 8.0, so it'll have to
wait until the tree re-opens for 8.1.

thanks
-- PMM