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

[Eugenio Perez Martin]

On Mon, Feb 28, 2022 at 3:32 AM Jason Wang <jasowang@redhat.com> wrote:
>
> 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 :)
>

Yes, I uncommented that part by mistake in git-publish and I'm still
paying the consequences.

Deleting right now so I don't forget anymore.

Thanks!

> 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
> >
> >
>