-.. BSD LICENSE
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-
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- notice, this list of conditions and the following disclaimer in
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- distribution.
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-
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+.. SPDX-License-Identifier: BSD-3-Clause
+ Copyright(c) 2010-2016 Intel Corporation.
Vhost Library
=============
Vhost API Overview
------------------
-The following is an overview of the Vhost API functions:
+The following is an overview of some key Vhost API functions:
* ``rte_vhost_driver_register(path, flags)``
* 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.
- The 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.
-* ``rte_vhost_driver_session_start()``
+ * 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
+ default.
+
+ Enabling this flag makes possible to use guest vIOMMU to protect vhost
+ from accessing memory the virtio device isn't allowed to, when the feature
+ is negotiated and an IOMMU device is declared.
+
+ However, this feature enables vhost-user's reply-ack protocol feature,
+ which implementation is buggy in Qemu v2.7.0-v2.9.0 when doing multiqueue.
+ 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.
- This function starts the vhost session loop to handle vhost messages. It
- starts an infinite loop, therefore it should be called in a dedicated
- thread.
+* ``rte_vhost_driver_set_features(path, features)``
-* ``rte_vhost_driver_callback_register(virtio_net_device_ops)``
+ This function sets the feature bits the vhost-user driver supports. The
+ vhost-user driver could be vhost-user net, yet it could be something else,
+ say, vhost-user SCSI.
+
+* ``rte_vhost_driver_callback_register(path, vhost_device_ops)``
This function registers a set of callbacks, to let DPDK applications take
the appropriate action when some events happen. The following events are
* ``new_device(int vid)``
- This callback is invoked when a virtio net device becomes ready. ``vid``
- is the virtio net device ID.
+ This callback is invoked when a virtio device becomes ready. ``vid``
+ is the vhost device ID.
* ``destroy_device(int vid)``
- This callback is invoked when a virtio net device shuts down (or when the
- vhost connection is broken).
+ This callback is invoked when a virtio device is paused or shut down.
* ``vring_state_changed(int vid, uint16_t queue_id, int enable)``
This callback is invoked when a specific queue's state is changed, for
example to enabled or disabled.
+ * ``features_changed(int vid, uint64_t features)``
+
+ This callback is invoked when the features is changed. For example,
+ ``VHOST_F_LOG_ALL`` will be set/cleared at the start/end of live
+ migration, respectively.
+
+ * ``new_connection(int vid)``
+
+ This callback is invoked on new vhost-user socket connection. If DPDK
+ acts as the server the device should not be deleted before
+ ``destroy_connection`` callback is received.
+
+ * ``destroy_connection(int vid)``
+
+ This callback is invoked when vhost-user socket connection is closed.
+ It indicates that device with id ``vid`` is no longer in use and can be
+ safely deleted.
+
+* ``rte_vhost_driver_disable/enable_features(path, features))``
+
+ This function disables/enables some features. For example, it can be used to
+ disable mergeable buffers and TSO features, which both are enabled by
+ default.
+
+* ``rte_vhost_driver_start(path)``
+
+ This function triggers the vhost-user negotiation. It should be invoked at
+ the end of initializing a vhost-user driver.
+
* ``rte_vhost_enqueue_burst(vid, queue_id, pkts, count)``
Transmits (enqueues) ``count`` packets from host to guest.
Receives (dequeues) ``count`` packets from guest, and stored them at ``pkts``.
-* ``rte_vhost_feature_disable/rte_vhost_feature_enable(feature_mask)``
+* ``rte_vhost_crypto_create(vid, cryptodev_id, sess_mempool, socket_id)``
- This function disables/enables some features. For example, it can be used to
- disable mergeable buffers and TSO features, which both are enabled by
- default.
+ As an extension of new_device(), this function adds virtio-crypto workload
+ acceleration capability to the device. All crypto workload is processed by
+ DPDK cryptodev with the device ID of ``cryptodev_id``.
+
+* ``rte_vhost_crypto_free(vid)``
+
+ Frees the memory and vhost-user message handlers created in
+ rte_vhost_crypto_create().
+
+* ``rte_vhost_crypto_fetch_requests(vid, queue_id, ops, nb_ops)``
+
+ Receives (dequeues) ``nb_ops`` virtio-crypto requests from guest, parses
+ them to DPDK Crypto Operations, and fills the ``ops`` with parsing results.
+
+* ``rte_vhost_crypto_finalize_requests(queue_id, ops, nb_ops)``
+
+ After the ``ops`` are dequeued from Cryptodev, finalizes the jobs and
+ notifies the guest(s).
+
+* ``rte_vhost_crypto_set_zero_copy(vid, option)``
+ Enable or disable zero copy feature of the vhost crypto backend.
Vhost-user Implementations
--------------------------
When the socket connection is closed, vhost will destroy the device.
+Guest memory requirement
+------------------------
+
+* Memory pre-allocation
+
+ For non-zerocopy, guest memory pre-allocation is not a must. This can help
+ save of memory. If users really want the guest memory to be pre-allocated
+ (e.g., for performance reason), we can add option ``-mem-prealloc`` when
+ starting QEMU. Or, we can lock all memory at vhost side which will force
+ memory to be allocated when mmap at vhost side; option --mlockall in
+ ovs-dpdk is an example in hand.
+
+ For zerocopy, we force the VM memory to be pre-allocated at vhost lib when
+ mapping the guest memory; and also we need to lock the memory to prevent
+ pages being swapped out to disk.
+
+* Memory sharing
+
+ Make sure ``share=on`` QEMU option is given. vhost-user will not work with
+ a QEMU version without shared memory mapping.
+
Vhost supported vSwitch reference
---------------------------------
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.