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
Unregister the async copy device channel from a vhost queue.
-* ``rte_vhost_submit_enqueue_burst(vid, queue_id, pkts, count)``
+* ``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.
* 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