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

[Michael S. Tsirkin]

On Tue, Mar 08, 2022 at 03:34:17PM +0800, Jason Wang wrote:
> On Tue, Mar 8, 2022 at 3:28 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Tue, Mar 08, 2022 at 03:14:35PM +0800, Jason Wang wrote:
> > > On Tue, Mar 8, 2022 at 3:11 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > >
> > > > On Tue, Mar 08, 2022 at 02:03:32PM +0800, Jason Wang wrote:
> > > > >
> > > > > 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
> > > >
> > > > A stable API for an incomplete feature is a problem imho.
> > >
> > > It should be "x-svq".
> >
> >
> > Well look at patch 15.
> 
> It's a bug that needs to be fixed.
> 
> >
> > > >
> > > >
> > > > > >
> > > > > > 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
> > > >
> > > > Well that's cutting it awfully close, and it's not really useful
> > > > at the current stage, is it?
> > >
> > > This allows vDPA to be migrated when using "x-svq=on".
> > > But anyhow it's
> > > experimental.
> >
> > it's less experimental than incomplete. It seems pretty clearly not
> > the way it will work down the road, we don't want svq involved
> > at all times.
> 
> Right, but SVQ could be used for other places e.g providing migration
> compatibility when the destination lacks some features.

In its current form? I don't see how.  Generally? Maybe but I suspect
we'll have to rework it completely for that.

> >
> > > >
> > > > The IOVA trick does not feel complete either.
> > >
> > > I don't get here. We don't use any IOVA trick as DPDK (it reserve IOVA
> > > for shadow vq) did. So we won't suffer from the issues of DPDK.
> > >
> > > Thanks
> >
> > Maybe I misundrstand how this all works.
> > I refer to all the iova_tree_alloc_map things.
> 
> It's a simple IOVA allocater actually. Anything wrong with that?

Not by itself but I'm not sure we can guarantee guest will not
attempt to use the IOVA addresses we are reserving down
the road.

> I'm fine with making it for the future release.
> 
> 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:
> > > > > > 20220302203012.3476835-1-eperezma@redhat.com/">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:
> > > > > > CAJaqyWfXHE0C54R_-OiwJzjC0gPpkE3eX0L8BeeZXGm1ERYPtA@mail.gmail.com/">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
> > > > > >
> > > >
> >