Re: [PATCH 00/31] vDPA shadow virtqueue

[Jason Wang]

在 2022/1/31 下午5:15, Eugenio Perez Martin 写道:
> On Fri, Jan 28, 2022 at 7:02 AM Jason Wang <jasowang@redhat.com> wrote:
> > 在 2022/1/22 上午4:27, Eugenio Pérez 写道:
> > > This series enables shadow virtqueue (SVQ) for vhost-vdpa devices. This
> > > is intended as a new method of tracking the memory the devices touch
> > > during a migration process: Instead of relay on vhost device's dirty
> > > logging capability, SVQ intercepts the VQ dataplane forwarding the
> > > descriptors between VM and device. This way qemu is the effective
> > > writer of guests memory, like in qemu's emulated virtio device
> > > operation.
> > >
> > > When SVQ is enabled qemu offers a new virtual address space to the
> > > device to read and write into, and it maps new vrings and the guest
> > > memory in it. SVQ also intercepts kicks and calls between the device
> > > and the guest. Used buffers relay would cause dirty memory being
> > > tracked, but at this RFC SVQ is not enabled on migration automatically.
> > >
> > > Thanks of being a buffers relay system, SVQ can be used also to
> > > communicate devices and drivers with different capabilities, like
> > > devices that only support packed vring and not split and old guests with
> > > no driver packed support.
> > >
> > > It is based on the ideas of DPDK SW assisted LM, in the series of
> > > DPDK's https://patchwork.dpdk.org/cover/48370/ . However, these does
> > > not map the shadow vq in guest's VA, but in qemu's.
> > >
> > > This version of SVQ is limited in the amount of features it can use with
> > > guest and device, because this series is already very big otherwise.
> > > Features like indirect or event_idx will be addressed in future series.
> > >
> > > SVQ needs to be enabled with cmdline parameter x-svq, like:
> > >
> > > -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0,x-svq=true
> > >
> > > In this version it cannot be enabled or disabled in runtime. Further
> > > series will remove this limitation and will enable it only for migration
> > > time.
> > >
> > > Some patches are intentionally very small to ease review, but they can
> > > be squashed if preferred.
> > >
> > > Patches 1-10 prepares the SVQ and QEMU to support both guest to device
> > > and device to guest notifications forwarding, with the extra qemu hop.
> > > That part can be tested in isolation if cmdline change is reproduced.
> > >
> > > Patches from 11 to 18 implement the actual buffer forwarding, but with
> > > no IOMMU support. It requires a vdpa device capable of addressing all
> > > qemu vaddr.
> > >
> > > Patches 19 to 23 adds the iommu support, so the device with address
> > > range limitations can access SVQ through this new virtual address space
> > > created.
> > >
> > > The rest of the series add the last pieces needed for migration.
> > >
> > > Comments are welcome.
> >
> > I wonder the performance impact. So performance numbers are more than
> > welcomed.
> Sure, I'll do it for the next revision. Since this one brings a decent
> amount of changes, I chose to collect the feedback first.


A simple single TCP_STREAM netperf test should be sufficient to give 
some basic understanding about the performance impact.

Thanks


> Thanks!
>
> > Thanks
> >
> >
> > > TODO:
> > > * Event, indirect, packed, and other features of virtio.
> > > * To separate buffers forwarding in its own AIO context, so we can
> > >     throw more threads to that task and we don't need to stop the main
> > >     event loop.
> > > * Support virtio-net control vq.
> > > * Proper documentation.
> > >
> > > Changes from v5 RFC:
> > > * Remove dynamic enablement of SVQ, making less dependent of the device.
> > > * Enable live migration if SVQ is enabled.
> > > * Fix SVQ when driver reset.
> > > * Comments addressed, specially in the iova area.
> > > * Rebase on latest master, adding multiqueue support (but no networking
> > >     control vq processing).
> > > v5 link:
> > > https://lists.gnu.org/archive/html/qemu-devel/2021-10/msg07250.html
> > >
> > > Changes from v4 RFC:
> > > * Support of allocating / freeing iova ranges in IOVA tree. Extending
> > >     already present iova-tree for that.
> > > * Proper validation of guest features. Now SVQ can negotiate a
> > >     different set of features with the device when enabled.
> > > * Support of host notifiers memory regions
> > > * Handling of SVQ full queue in case guest's descriptors span to
> > >     different memory regions (qemu's VA chunks).
> > > * Flush pending used buffers at end of SVQ operation.
> > > * QMP command now looks by NetClientState name. Other devices will need
> > >     to implement it's way to enable vdpa.
> > > * Rename QMP command to set, so it looks more like a way of working
> > > * Better use of qemu error system
> > > * Make a few assertions proper error-handling paths.
> > > * Add more documentation
> > > * Less coupling of virtio / vhost, that could cause friction on changes
> > > * Addressed many other small comments and small fixes.
> > >
> > > Changes from v3 RFC:
> > >     * Move everything to vhost-vdpa backend. A big change, this allowed
> > >       some cleanup but more code has been added in other places.
> > >     * More use of glib utilities, especially to manage memory.
> > > v3 link:
> > > https://lists.nongnu.org/archive/html/qemu-devel/2021-05/msg06032.html
> > >
> > > Changes from v2 RFC:
> > >     * Adding vhost-vdpa devices support
> > >     * Fixed some memory leaks pointed by different comments
> > > v2 link:
> > > https://lists.nongnu.org/archive/html/qemu-devel/2021-03/msg05600.html
> > >
> > > Changes from v1 RFC:
> > >     * Use QMP instead of migration to start SVQ mode.
> > >     * Only accepting IOMMU devices, closer behavior with target devices
> > >       (vDPA)
> > >     * Fix invalid masking/unmasking of vhost call fd.
> > >     * Use of proper methods for synchronization.
> > >     * No need to modify VirtIO device code, all of the changes are
> > >       contained in vhost code.
> > >     * Delete superfluous code.
> > >     * An intermediate RFC was sent with only the notifications forwarding
> > >       changes. It can be seen in
> > >       https://patchew.org/QEMU/20210129205415.876290-1-eperezma@redhat.com/
> > > v1 link:
> > > https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg05372.html
> > >
> > > Eugenio Pérez (20):
> > >         virtio: Add VIRTIO_F_QUEUE_STATE
> > >         virtio-net: Honor VIRTIO_CONFIG_S_DEVICE_STOPPED
> > >         virtio: Add virtio_queue_is_host_notifier_enabled
> > >         vhost: Make vhost_virtqueue_{start,stop} public
> > >         vhost: Add x-vhost-enable-shadow-vq qmp
> > >         vhost: Add VhostShadowVirtqueue
> > >         vdpa: Register vdpa devices in a list
> > >         vhost: Route guest->host notification through shadow virtqueue
> > >         Add vhost_svq_get_svq_call_notifier
> > >         Add vhost_svq_set_guest_call_notifier
> > >         vdpa: Save call_fd in vhost-vdpa
> > >         vhost-vdpa: Take into account SVQ in vhost_vdpa_set_vring_call
> > >         vhost: Route host->guest notification through shadow virtqueue
> > >         virtio: Add vhost_shadow_vq_get_vring_addr
> > >         vdpa: Save host and guest features
> > >         vhost: Add vhost_svq_valid_device_features to shadow vq
> > >         vhost: Shadow virtqueue buffers forwarding
> > >         vhost: Add VhostIOVATree
> > >         vhost: Use a tree to store memory mappings
> > >         vdpa: Add custom IOTLB translations to SVQ
> > >
> > > Eugenio Pérez (31):
> > >     vdpa: Reorder virtio/vhost-vdpa.c functions
> > >     vhost: Add VhostShadowVirtqueue
> > >     vdpa: Add vhost_svq_get_dev_kick_notifier
> > >     vdpa: Add vhost_svq_set_svq_kick_fd
> > >     vhost: Add Shadow VirtQueue kick forwarding capabilities
> > >     vhost: Route guest->host notification through shadow virtqueue
> > >     vhost: dd vhost_svq_get_svq_call_notifier
> > >     vhost: Add vhost_svq_set_guest_call_notifier
> > >     vhost-vdpa: Take into account SVQ in vhost_vdpa_set_vring_call
> > >     vhost: Route host->guest notification through shadow virtqueue
> > >     vhost: Add vhost_svq_valid_device_features to shadow vq
> > >     vhost: Add vhost_svq_valid_guest_features to shadow vq
> > >     vhost: Add vhost_svq_ack_guest_features to shadow vq
> > >     virtio: Add vhost_shadow_vq_get_vring_addr
> > >     vdpa: Add vhost_svq_get_num
> > >     vhost: pass queue index to vhost_vq_get_addr
> > >     vdpa: adapt vhost_ops callbacks to svq
> > >     vhost: Shadow virtqueue buffers forwarding
> > >     utils: Add internal DMAMap to iova-tree
> > >     util: Store DMA entries in a list
> > >     util: Add iova_tree_alloc
> > >     vhost: Add VhostIOVATree
> > >     vdpa: Add custom IOTLB translations to SVQ
> > >     vhost: Add vhost_svq_get_last_used_idx
> > >     vdpa: Adapt vhost_vdpa_get_vring_base to SVQ
> > >     vdpa: Clear VHOST_VRING_F_LOG at vhost_vdpa_set_vring_addr in SVQ
> > >     vdpa: Never set log_base addr if SVQ is enabled
> > >     vdpa: Expose VHOST_F_LOG_ALL on SVQ
> > >     vdpa: Make ncs autofree
> > >     vdpa: Move vhost_vdpa_get_iova_range to net/vhost-vdpa.c
> > >     vdpa: Add x-svq to NetdevVhostVDPAOptions
> > >
> > >    qapi/net.json                      |   5 +-
> > >    hw/virtio/vhost-iova-tree.h        |  27 +
> > >    hw/virtio/vhost-shadow-virtqueue.h |  46 ++
> > >    include/hw/virtio/vhost-vdpa.h     |   7 +
> > >    include/qemu/iova-tree.h           |  17 +
> > >    hw/virtio/vhost-iova-tree.c        | 157 ++++++
> > >    hw/virtio/vhost-shadow-virtqueue.c | 761 +++++++++++++++++++++++++++++
> > >    hw/virtio/vhost-vdpa.c             | 740 ++++++++++++++++++++++++----
> > >    hw/virtio/vhost.c                  |   6 +-
> > >    net/vhost-vdpa.c                   |  58 ++-
> > >    util/iova-tree.c                   | 161 +++++-
> > >    hw/virtio/meson.build              |   2 +-
> > >    12 files changed, 1852 insertions(+), 135 deletions(-)
> > >    create mode 100644 hw/virtio/vhost-iova-tree.h
> > >    create mode 100644 hw/virtio/vhost-shadow-virtqueue.h
> > >    create mode 100644 hw/virtio/vhost-iova-tree.c
> > >    create mode 100644 hw/virtio/vhost-shadow-virtqueue.c