[5/6] doc: document packed virtqueue for virtio
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Document the packed virtqueue layout support in virtio net PMD.
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
---
doc/guides/nics/virtio.rst | 63 ++++++++++++++++++++++++++++----------
1 file changed, 47 insertions(+), 16 deletions(-)
Comments
On 8/13/19 4:07 AM, Tiwei Bie wrote:
> Document the packed virtqueue layout support in virtio net PMD.
>
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> ---
> doc/guides/nics/virtio.rst | 63 ++++++++++++++++++++++++++++----------
> 1 file changed, 47 insertions(+), 16 deletions(-)
>
> diff --git a/doc/guides/nics/virtio.rst b/doc/guides/nics/virtio.rst
> index 993e691f5..011954ff6 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))
>
Side note: One day, we may consider to enable it by default.
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
@@ -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))