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-rw-r--r--doc/guides/nics/enic.rst53
1 files changed, 48 insertions, 5 deletions
diff --git a/doc/guides/nics/enic.rst b/doc/guides/nics/enic.rst
index 8170286..bff5c77 100644
--- a/doc/guides/nics/enic.rst
+++ b/doc/guides/nics/enic.rst
@@ -59,11 +59,31 @@ Configuration information
- **Number of Queues**
- The maximum number of receive and transmit queues are configurable on a per
- vNIC basis through the Cisco UCS Manager (CIMC or UCSM). These values
- should be configured to be greater than or equal to the nb_rx_q and nb_tx_q
- parameters expected to used in the call to the rte_eth_dev_configure()
- function.
+ The maximum number of receive queues (RQs), work queues (WQs) and
+ completion queues (CQs) are configurable on a per vNIC basis
+ through the Cisco UCS Manager (CIMC or UCSM).
+
+ These values should be configured as follows:
+
+ - The number of WQs should be greater or equal to the value of the
+ expected nb_tx_q parameter in the call to the
+ rte_eth_dev_configure()
+
+ - The number of RQs configured in the vNIC should be greater or
+ equal to *twice* the value of the expected nb_rx_q parameter in
+ the call to rte_eth_dev_configure(). With the addition of rx
+ scatter, a pair of RQs on the vnic is needed for each receive
+ queue used by DPDK, even if rx scatter is not being used.
+ Having a vNIC with only 1 RQ is not a valid configuration, and
+ will fail with an error message.
+
+ - The number of CQs should set so that there is one CQ for each
+ WQ, and one CQ for each pair of RQs.
+
+ For example: If the application requires 3 Rx queues, and 3 Tx
+ queues, the vNIC should be configured to have at least 3 WQs, 6
+ RQs (3 pairs), and 6 CQs (3 for use by WQs + 3 for use by the 3
+ pairs of RQs).
- **Size of Queues**
@@ -71,6 +91,29 @@ Configuration information
a per vNIC bases via the UCS Manager and should be greater than or equal to
the nb_rx_desc and nb_tx_desc parameters expected to be used in the calls
to rte_eth_rx_queue_setup() and rte_eth_tx_queue_setup() respectively.
+ An application requesting more than the set size will be limited to that
+ size.
+
+ Unless there is a lack of resources due to creating many vNICs, it
+ is recommended that the WQ and RQ sizes be set to the maximum. This
+ gives the application the greatest amount of flexibility in its
+ queue configuration.
+
+ - *Note*: Since the introduction of rx scatter, for performance
+ reasons, this PMD uses two RQs on the vNIC per receive queue in
+ DPDK. One RQ holds descriptors for the start of a packet the
+ second RQ holds the descriptors for the rest of the fragments of
+ a packet. This means that the nb_rx_desc parameter to
+ rte_eth_rx_queue_setup() can be a greater than 4096. The exact
+ amount will depend on the size of the mbufs being used for
+ receives, and the MTU size.
+
+ For example: If the mbuf size is 2048, and the MTU is 9000, then
+ receiving a full size packet will take 5 descriptors, 1 from the
+ start of packet queue, and 4 from the second queue. Assuming
+ that the RQ size was set to the maximum of 4096, then the
+ application can specify up to 1024 + 4096 as the nb_rx_desc
+ parameter to rte_eth_rx_queue_setup().
- **Interrupts**