On Sun, Feb 27, 2022 at 9:42 PM Eugenio Pérez <eperezma@xxxxxxxxxx> 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@xxxxxxxxxx/ > > 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@xxxxxxxxxx/ > 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 > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
