Re: [PATCH v5 00/15] vDPA shadow virtqueue

[Jason Wang <jasowang@redhat.com>]

在 2022/3/7 下午11:33, Eugenio Pérez 写道:
> 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.
>
> SVQ needs to be enabled with cmdline:
>
> -netdev type=vhost-vdpa,vhostdev=vhost-vdpa-0,id=vhost-vdpa0,svq=on
>
> 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 ~9009.96Mbps:
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 131072  16384  16384    30.01    9061.03
> 131072  16384  16384    30.01    8962.94
> 131072  16384  16384    30.01    9005.92
>
> To enable SVQ buffers forwarding reduce throughput to about
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 131072  16384  16384    30.01    7689.72
> 131072  16384  16384    30.00    7752.07
> 131072  16384  16384    30.01    7750.30
>
> However, many performance improvements were left out of this series for
> simplicity, so difference should shrink in the future.
>
> Comments are welcome.


Hi Michael:

What do you think of this series? It looks good to me as a start. The 
feature could only be enabled as a dedicated parameter. If you're ok, 
I'd try to make it for 7.0.

Thanks


>
> TODO on 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 v4:
> * Iterate iova->hva tree instead on maintain own tree so we support HVA
>    overlaps.
> * Fix: Errno completion at failure.
> * Rename x-svq to svq, so changes to stable does not affect cmdline parameter.
>
> Changes from v3:
> * Add @unstable feature to NetdevVhostVDPAOptions.x-svq.
> * Fix uncomplete mapping (by 1 byte) of memory regions if svq is enabled.
> v3 link:
> https://lore.kernel.org/qemu-devel/20220302203012.3476835-1-eperezma@redhat.com/
>
> Changes from v2:
> * Less assertions and more error handling in iova tree code.
> * Better documentation, both fixing errors and making @param: format
> * Homogeneize SVQ avail_idx_shadow and shadow_used_idx to make shadow a
>    prefix at both times.
> * Fix: Fo not use VirtQueueElement->len field, track separatedly.
> * Split vhost_svq_{enable,disable}_notification, so the code looks more
>    like the kernel driver code.
> * Small improvements.
> v2 link:
> https://lore.kernel.org/all/CAJaqyWfXHE0C54R_-OiwJzjC0gPpkE3eX0L8BeeZXGm1ERYPtA@mail.gmail.com/
>
> 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
>
> Eugenio Pérez (15):
>    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_svq_get_vring_addr
>    vdpa: adapt vhost_ops callbacks to svq
>    vhost: Shadow virtqueue buffers forwarding
>    util: Add iova_tree_alloc_map
>    util: add iova_tree_find_iova
>    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                      |   8 +-
>   hw/virtio/vhost-iova-tree.h        |  27 ++
>   hw/virtio/vhost-shadow-virtqueue.h |  87 ++++
>   include/hw/virtio/vhost-vdpa.h     |   8 +
>   include/qemu/iova-tree.h           |  38 +-
>   hw/virtio/vhost-iova-tree.c        | 110 +++++
>   hw/virtio/vhost-shadow-virtqueue.c | 637 +++++++++++++++++++++++++++++
>   hw/virtio/vhost-vdpa.c             | 525 +++++++++++++++++++++++-
>   net/vhost-vdpa.c                   |  48 ++-
>   util/iova-tree.c                   | 169 ++++++++
>   hw/virtio/meson.build              |   2 +-
>   11 files changed, 1633 insertions(+), 26 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
>

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