This reconnect option is enabled by default. However, it can be turned off
by setting this flag.
- - ``RTE_VHOST_USER_DEQUEUE_ZERO_COPY``
-
- Dequeue zero copy will be enabled when this flag is set. It is disabled by
- default.
-
- There are some truths (including limitations) you might want to know while
- setting this flag:
-
- * zero copy is not good for small packets (typically for packet size below
- 512).
-
- * zero copy is really good for VM2VM case. For iperf between two VMs, the
- boost could be above 70% (when TSO 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.
-
- 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.
-
- When dequeue zero copy is enabled, the guest phys address and host phys
- address mapping has to be established. Using non-huge pages means far
- more page segments. To make it simple, DPDK vhost does a linear search
- 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.
-
- * The consumer of zero copy mbufs should consume these mbufs as soon as
- possible, otherwise it may block the operations in vhost.
-
- ``RTE_VHOST_USER_IOMMU_SUPPORT``
IOMMU support will be enabled when this flag is set. It is disabled by
It is disabled by default.
+ - ``RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS``
+
+ Since v16.04, the vhost library forwards checksum and gso requests for
+ packets received from a virtio driver by filling Tx offload metadata in
+ the mbuf. This behavior is inconsistent with other drivers but it is left
+ untouched for existing applications that might rely on it.
+
+ This flag disables the legacy behavior and instead ask vhost to simply
+ populate Rx offload metadata in the mbuf.
+
+ It is disabled by default.
+
* ``rte_vhost_driver_set_features(path, features)``
This function sets the feature bits the vhost-user driver supports. The
Enable or disable zero copy feature of the vhost crypto backend.
-* ``rte_vhost_async_channel_register(vid, queue_id, features, ops)``
-
- Register a vhost queue with async copy device channel.
- Following device ``features`` must be specified together with the
- registration:
-
- * ``async_inorder``
+* ``rte_vhost_async_channel_register(vid, queue_id, config, ops)``
- Async copy device can guarantee the ordering of copy completion
- sequence. Copies are completed in the same order with that at
- the submission time.
+ Register an async copy device channel for a vhost queue after vring
+ is enabled. Following device ``config`` must be specified together
+ with the registration:
- Currently, only ``async_inorder`` capable device is supported by vhost.
+ * ``features``
- * ``async_threshold``
+ This field is used to specify async copy device features.
- The copy length (in bytes) below which CPU copy will be used even if
- applications call async vhost APIs to enqueue/dequeue data.
+ ``RTE_VHOST_ASYNC_INORDER`` represents the async copy device can
+ guarantee the order of copy completion is the same as the order
+ of copy submission.
- Typical value is 512~1024 depending on the async device capability.
+ Currently, only ``RTE_VHOST_ASYNC_INORDER`` capable device is
+ supported by vhost.
Applications must provide following ``ops`` callbacks for vhost lib to
work with the async copy devices:
vhost invokes this function to get the copy data completed by async
devices.
+* ``rte_vhost_async_channel_register_thread_unsafe(vid, queue_id, config, ops)``
+
+ Register an async copy device channel for a vhost queue without
+ performing any locking.
+
+ This function is only safe to call in vhost callback functions
+ (i.e., struct vhost_device_ops).
+
* ``rte_vhost_async_channel_unregister(vid, queue_id)``
Unregister the async copy device channel from a vhost queue.
+ Unregistration will fail, if the vhost queue has in-flight
+ packets that are not completed.
+
+ Unregister async copy devices in vring_state_changed() may
+ fail, as this API tries to acquire the spinlock of vhost
+ queue. The recommended way is to unregister async copy
+ devices for all vhost queues in destroy_device(), when a
+ virtio device is paused or shut down.
-* ``rte_vhost_submit_enqueue_burst(vid, queue_id, pkts, count)``
+* ``rte_vhost_async_channel_unregister_thread_unsafe(vid, queue_id)``
+
+ Unregister the async copy device channel for a vhost queue without
+ performing any locking.
+
+ This function is only safe to call in vhost callback functions
+ (i.e., struct vhost_device_ops).
+
+* ``rte_vhost_submit_enqueue_burst(vid, queue_id, pkts, count, comp_pkts, comp_count)``
Submit an enqueue request to transmit ``count`` packets from host to guest
- by async data path. Enqueue is not guaranteed to finish upon the return of
- this API call.
+ by async data path. Successfully enqueued packets can be transfer completed
+ or being occupied by DMA engines; transfer completed packets are returned in
+ ``comp_pkts``, but others are not guaranteed to finish, when this API
+ call returns.
Applications must not free the packets submitted for enqueue until the
packets are completed.
Poll enqueue completion status from async data path. Completed packets
are returned to applications through ``pkts``.
+* ``rte_vhost_async_get_inflight(vid, queue_id)``
+
+ This function returns the amount of in-flight packets for the vhost
+ queue using async acceleration.
+
+* ``rte_vhost_clear_queue_thread_unsafe(vid, queue_id, **pkts, count)``
+
+ Clear inflight packets which are submitted to DMA engine in vhost async data
+ path. Completed packets are returned to applications through ``pkts``.
+
Vhost-user Implementations
--------------------------
* Memory pre-allocation
- For non-zerocopy non-async data path, guest memory pre-allocation is not a
+ For non-async data path, 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 async and zerocopy data path, 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.
+ For async data path, 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
git.droids-corp.org / dpdk.git / blobdiff