* zero copy is really good for VM2VM case. For iperf between two VMs, the
boost could be above 70% (when TSO is enableld).
- * for VM2NIC case, the ``nb_tx_desc`` has to be small enough: <= 64 if virtio
- indirect feature is not enabled and <= 128 if it is enabled.
+ * For zero copy in VM2NIC case, guest Tx used vring may be starved if the
+ PMD driver consume the mbuf but not release them timely.
- This is because when dequeue zero copy is enabled, guest Tx used vring will
- be updated only when corresponding mbuf is freed. Thus, the nb_tx_desc
- has to be small enough so that the PMD driver will run out of available
- Tx descriptors and free mbufs timely. Otherwise, guest Tx vring would be
- starved.
+ For example, i40e driver has an optimization to maximum NIC pipeline which
+ postpones returning transmitted mbuf until only tx_free_threshold free
+ descs left. The virtio TX used ring will be starved if the formula
+ (num_i40e_tx_desc - num_virtio_tx_desc > tx_free_threshold) is true, since
+ i40e will not return back mbuf.
+
+ A performance tip for tuning zero copy in VM2NIC case is to adjust the
+ frequency of mbuf free (i.e. adjust tx_free_threshold of i40e driver) to
+ balance consumer and producer.
* Guest memory should be backended with huge pages to achieve better
performance. Using 1G page size is the best.
of those segments, thus the fewer the segments, the quicker we will get
the mapping. NOTE: we may speed it by using tree searching in future.
+ * zero copy can not work when using vfio-pci with iommu mode currently, this
+ is because we don't setup iommu dma mapping for guest memory. If you have
+ to use vfio-pci driver, please insert vfio-pci kernel module in noiommu
+ mode.
+
- ``RTE_VHOST_USER_IOMMU_SUPPORT``
IOMMU support will be enabled when this flag is set. It is disabled by
Enabling this flag with these Qemu version results in Qemu being blocked
when multiple queue pairs are declared.
+ - ``RTE_VHOST_USER_POSTCOPY_SUPPORT``
+
+ Postcopy live-migration support will be enabled when this flag is set.
+ It is disabled by default.
+
+ Enabling this flag should only be done when the calling application does
+ not pre-fault the guest shared memory, otherwise migration would fail.
+
* ``rte_vhost_driver_set_features(path, features)``
This function sets the feature bits the vhost-user driver supports. The
For more vhost details and how to support vhost in vSwitch, please refer to
the vhost example in the DPDK Sample Applications Guide.
+
+Vhost data path acceleration (vDPA)
+-----------------------------------
+
+vDPA supports selective datapath in vhost-user lib by enabling virtio ring
+compatible devices to serve virtio driver directly for datapath acceleration.
+
+``rte_vhost_driver_attach_vdpa_device`` is used to configure the vhost device
+with accelerated backend.
+
+Also vhost device capabilities are made configurable to adopt various devices.
+Such capabilities include supported features, protocol features, queue number.
+
+Finally, a set of device ops is defined for device specific operations:
+
+* ``get_queue_num``
+
+ Called to get supported queue number of the device.
+
+* ``get_features``
+
+ Called to get supported features of the device.
+
+* ``get_protocol_features``
+
+ Called to get supported protocol features of the device.
+
+* ``dev_conf``
+
+ Called to configure the actual device when the virtio device becomes ready.
+
+* ``dev_close``
+
+ Called to close the actual device when the virtio device is stopped.
+
+* ``set_vring_state``
+
+ Called to change the state of the vring in the actual device when vring state
+ changes.
+
+* ``set_features``
+
+ Called to set the negotiated features to device.
+
+* ``migration_done``
+
+ Called to allow the device to response to RARP sending.
+
+* ``get_vfio_group_fd``
+
+ Called to get the VFIO group fd of the device.
+
+* ``get_vfio_device_fd``
+
+ Called to get the VFIO device fd of the device.
+
+* ``get_notify_area``
+
+ Called to get the notify area info of the queue.
git.droids-corp.org / dpdk.git / blobdiff