Re: [PATCH v2 00/14] vDPA shadow virtqueue

[Jason Wang]

On Sun, Feb 27, 2022 at 9:42 PM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> This series enable 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 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.
>
> This effectively means that vDPA device passthrough is intercepted by
> qemu. While SVQ should only be enabled at migration time, the switching
> from regular mode to SVQ mode is left for a future series.
>
> 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.
>
> For qemu to use shadow virtqueues the guest virtio driver must not use
> features like event_idx, indirect descriptors, packed and in_order.
> These features are easy to implement on top of this base, but is left
> for a future series for simplicity.
>
> SVQ needs to be enabled at qemu start time with vdpa cmdline parameter:
>
> -netdev type=vhost-vdpa,vhostdev=vhost-vdpa-0,id=vhost-vdpa0,x-svq=off
>
> The first three patches enables notifications forwarding with
> assistance of qemu. It's easy to enable only this if the relevant
> cmdline part of the last patch is applied on top of these.
>
> Next four patches implement the actual buffer forwarding. However,
> address are not translated from HVA so they will need a host device with
> an iommu allowing them to access all of the HVA range.
>
> The last part of the series uses properly the host iommu, so qemu
> creates a new iova address space in the device's range and translates
> the buffers in it. Finally, it adds the cmdline parameter.
>
> Some simple performance tests with netperf were done. They used a nested
> guest with vp_vdpa, vhost-kernel at L0 host. Starting with no svq and a
> baseline average of ~9980.13Mbps:
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
>
> 131072  16384  16384    30.01    9910.61
> 131072  16384  16384    30.00    10030.94
> 131072  16384  16384    30.01    9998.84
>
> To enable the notifications interception reduced performance to an
> average of ~9577.73Mbit/s:
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
>
> 131072  16384  16384    30.00    9563.03
> 131072  16384  16384    30.01    9626.65
> 131072  16384  16384    30.01    9543.51
>
> Finally, to enable buffers forwarding reduced the throughput again to
> ~8902.92Mbit/s:
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
>
> 131072  16384  16384    30.01    8643.19
> 131072  16384  16384    30.01    9033.56
> 131072  16384  16384    30.01    9032.02
>
> However, many performance improvements were left out of this series for
> simplicity, so difference if performance should shrink in the future.

I think the performance should be acceptable as a start.

>
> Comments are welcome.
>
> TODO in future series:
> * Event, indirect, packed, and others features of virtio.
> * To support different set of features between the device<->SVQ and the
>   SVQ<->guest communication.
> * Support of device host notifier memory regions.
> * To sepparate 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 multiqueue virtio-net vdpa.
> * Proper documentation.
>
> Changes from v1:
> * Feature set at device->SVQ is now the same as SVQ->guest.
> * Size of SVQ is not max available device size anymore, but guest's
>   negotiated.
> * Add VHOST_FILE_UNBIND kick and call fd treatment.
> * Make SVQ a public struct
> * Come back to previous approach to iova-tree
> * Some assertions are now fail paths. Some errors are now log_guest.
> * Only mask _F_LOG feature at vdpa_set_features svq enable path.
> * Refactor some errors and messages. Add missing error unwindings.
> * Add memory barrier at _F_NO_NOTIFY set.
> * Stop checking for features flags out of transport range.
> v1 link:
> https://lore.kernel.org/virtualization/7d86c715-6d71-8a27-91f5-8d47b71e3201@redhat.com/
>
> 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

This list seems wrong btw :)

Thanks

>
> Eugenio Pérez (14):
>   vhost: Add VhostShadowVirtqueue
>   vhost: Add Shadow VirtQueue kick forwarding capabilities
>   vhost: Add Shadow VirtQueue call forwarding capabilities
>   vhost: Add vhost_svq_valid_features to shadow vq
>   virtio: Add vhost_shadow_vq_get_vring_addr
>   vdpa: adapt vhost_ops callbacks to svq
>   vhost: Shadow virtqueue buffers forwarding
>   util: Add iova_tree_alloc
>   vhost: Add VhostIOVATree
>   vdpa: Add custom IOTLB translations to SVQ
>   vdpa: Adapt vhost_vdpa_get_vring_base to SVQ
>   vdpa: Never set log_base addr if SVQ is enabled
>   vdpa: Expose VHOST_F_LOG_ALL on SVQ
>   vdpa: Add x-svq to NetdevVhostVDPAOptions
>
>  qapi/net.json                      |   5 +-
>  hw/virtio/vhost-iova-tree.h        |  27 ++
>  hw/virtio/vhost-shadow-virtqueue.h |  90 ++++
>  include/hw/virtio/vhost-vdpa.h     |   8 +
>  include/qemu/iova-tree.h           |  18 +
>  hw/virtio/vhost-iova-tree.c        | 155 +++++++
>  hw/virtio/vhost-shadow-virtqueue.c | 632 +++++++++++++++++++++++++++++
>  hw/virtio/vhost-vdpa.c             | 551 ++++++++++++++++++++++++-
>  net/vhost-vdpa.c                   |  48 ++-
>  util/iova-tree.c                   | 133 ++++++
>  hw/virtio/meson.build              |   2 +-
>  11 files changed, 1644 insertions(+), 25 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
>
> --
> 2.27.0
>
>