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Diffstat (limited to 'doc/guides/prog_guide/vhost_lib.rst')
| -rw-r--r-- | doc/guides/prog_guide/vhost_lib.rst | 128 |
1 files changed, 121 insertions, 7 deletions
diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst index 18227b6a..77af4d77 100644 --- a/doc/guides/prog_guide/vhost_lib.rst +++ b/doc/guides/prog_guide/vhost_lib.rst @@ -65,14 +65,18 @@ The following is an overview of some key Vhost API functions: * 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. @@ -83,6 +87,11 @@ The following is an overview of some key Vhost API functions: 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 @@ -160,6 +169,31 @@ The following is an overview of some key Vhost API functions: Receives (dequeues) ``count`` packets from guest, and stored them at ``pkts``. +* ``rte_vhost_crypto_create(vid, cryptodev_id, sess_mempool, socket_id)`` + + 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 -------------------------- @@ -214,8 +248,88 @@ the vhost device from the data plane. 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. |