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authorTiwei Bie <tiwei.bie@intel.com>2019-08-13 10:07:29 +0800
committerFerruh Yigit <ferruh.yigit@intel.com>2019-09-06 17:32:42 +0200
commitab600834dbc085dc2cc46a8b0fc262639ed965be (patch)
tree52aaeec011f8cc5198a388b0a3b70920ff8ec9ad
parent14d1fad5650c2bef8d1ab494a43fc823740f2470 (diff)
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doc: add packed virtqueue in virtio guide
Document the packed virtqueue layout support in virtio net PMD. Signed-off-by: Tiwei Bie <tiwei.bie@intel.com> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
-rw-r--r--doc/guides/nics/virtio.rst63
1 files changed, 47 insertions, 16 deletions
diff --git a/doc/guides/nics/virtio.rst b/doc/guides/nics/virtio.rst
index 993e691..011954f 100644
--- a/doc/guides/nics/virtio.rst
+++ b/doc/guides/nics/virtio.rst
@@ -24,15 +24,19 @@ standard qemu vhost back end and vhost kni back end.
Virtio Implementation in DPDK
-----------------------------
-For details about the virtio spec, refer to Virtio PCI Card Specification written by Rusty Russell.
+For details about the virtio spec, refer to the latest
+`VIRTIO (Virtual I/O) Device Specification
+<https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio>`_.
-As a PMD, virtio provides packet reception and transmission callbacks virtio_recv_pkts and virtio_xmit_pkts.
+As a PMD, virtio provides packet reception and transmission callbacks.
-In virtio_recv_pkts, index in range [vq->vq_used_cons_idx , vq->vq_ring.used->idx) in vring is available for virtio to burst out.
+In Rx, packets described by the used descriptors in vring are available
+for virtio to burst out.
-In virtio_xmit_pkts, same index range in vring is available for virtio to clean.
-Virtio will enqueue to be transmitted packets into vring, advance the vq->vq_ring.avail->idx,
-and then notify the host back end if necessary.
+In Tx, packets described by the used descriptors in vring are available
+for virtio to clean. Virtio will enqueue to be transmitted packets into
+vring, make them available to the device, and then notify the host back
+end if necessary.
Features and Limitations of virtio PMD
--------------------------------------
@@ -201,37 +205,52 @@ The packet transmission flow is:
Virtio PMD Rx/Tx Callbacks
--------------------------
-Virtio driver has 4 Rx callbacks and 2 Tx callbacks.
+Virtio driver has 6 Rx callbacks and 3 Tx callbacks.
Rx callbacks:
#. ``virtio_recv_pkts``:
- Regular version without mergeable Rx buffer support.
+ Regular version without mergeable Rx buffer support for split virtqueue.
#. ``virtio_recv_mergeable_pkts``:
- Regular version with mergeable Rx buffer support.
+ Regular version with mergeable Rx buffer support for split virtqueue.
#. ``virtio_recv_pkts_vec``:
Vector version without mergeable Rx buffer support, also fixes the available
- ring indexes and uses vector instructions to optimize performance.
+ ring indexes and uses vector instructions to optimize performance for split
+ virtqueue.
#. ``virtio_recv_pkts_inorder``:
- In-order version with mergeable and non-mergeable Rx buffer support.
+ In-order version with mergeable and non-mergeable Rx buffer support
+ for split virtqueue.
+
+#. ``virtio_recv_pkts_packed``:
+ Regular and in-order version without mergeable Rx buffer support for
+ packed virtqueue.
+
+#. ``virtio_recv_mergeable_pkts_packed``:
+ Regular and in-order version with mergeable Rx buffer support for packed
+ virtqueue.
Tx callbacks:
#. ``virtio_xmit_pkts``:
- Regular version.
+ Regular version for split virtqueue.
#. ``virtio_xmit_pkts_inorder``:
- In-order version.
+ In-order version for split virtqueue.
+
+#. ``virtio_xmit_pkts_packed``:
+ Regular and in-order version for packed virtqueue.
By default, the non-vector callbacks are used:
-* For Rx: If mergeable Rx buffers is disabled then ``virtio_recv_pkts`` is
- used; otherwise ``virtio_recv_mergeable_pkts``.
+* For Rx: If mergeable Rx buffers is disabled then ``virtio_recv_pkts``
+ or ``virtio_recv_pkts_packed`` will be used, otherwise
+ ``virtio_recv_mergeable_pkts`` or ``virtio_recv_mergeable_pkts_packed``
+ will be used.
-* For Tx: ``virtio_xmit_pkts``.
+* For Tx: ``virtio_xmit_pkts`` or ``virtio_xmit_pkts_packed`` will be used.
Vector callbacks will be used when:
@@ -242,6 +261,8 @@ The corresponding callbacks are:
* For Rx: ``virtio_recv_pkts_vec``.
+There is no vector callbacks for packed virtqueue for now.
+
Example of using the vector version of the virtio poll mode driver in
``testpmd``::
@@ -250,10 +271,15 @@ Example of using the vector version of the virtio poll mode driver in
In-order callbacks only work on simulated virtio user vdev.
+For split virtqueue:
+
* For Rx: If in-order is enabled then ``virtio_recv_pkts_inorder`` is used.
* For Tx: If in-order is enabled then ``virtio_xmit_pkts_inorder`` is used.
+For packed virtqueue, the default callbacks already support the
+in-order feature.
+
Interrupt mode
--------------
@@ -372,3 +398,8 @@ Below devargs are supported by the virtio-user vdev:
It is used to enable virtio device in-order feature.
(Default: 1 (enabled))
+
+#. ``packed_vq``:
+
+ It is used to enable virtio device packed virtqueue feature.
+ (Default: 0 (disabled))