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 at 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 at
redhat.com> wrote:
> > > >
> > > > On Tue, Mar 08, 2022 at 02:03:32PM +0800, Jason Wang wrote:
> > > > >
> > > > > ? 2022/3/7 ??11:33, Eugenio P?rez ??:
> > > > > > 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:
> > > > > >
https://lore.kernel.org/qemu-devel/20220302203012.3476835-1-eperezma at
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
at 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 at
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 at redhat.com/
> > > > > > v1 link:
> > > > > >
https://lists.gnu.org/archive/html/qemu-devel/2020-11/msg05372.html
> > > > > >
> > > > > > Eugenio P?rez (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 P?rez (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
> > > > > >
> > > >
> >