To achieve optimal performance, overall software design choices and pure software optimization techniques must be considered and
balanced against available low-level hardware-based optimization features (CPU cache properties, bus speed, NIC PCI bandwidth, and so on).
-The case of packet transmission is an example of this software/ hardware tradeoff issue when optimizing burst-oriented network packet processing engines.
+The case of packet transmission is an example of this software/hardware tradeoff issue when optimizing burst-oriented network packet processing engines.
In the initial case, the PMD could export only an rte_eth_tx_one function to transmit one packet at a time on a given queue.
On top of that, one can easily build an rte_eth_tx_burst function that loops invoking the rte_eth_tx_one function to transmit several packets at a time.
However, an rte_eth_tx_burst function is effectively implemented by the PMD to minimize the driver-level transmit cost per packet through the following optimizations:
Other features such as the L3/L4 5-Tuple packet filtering feature of a port can be configured in the same way.
Ethernet* flow control (pause frame) can be configured on the individual port.
Refer to the testpmd source code for details.
-Also, L4 (UDP/TCP/ SCTP) checksum offload by the NIC can be enabled for an individual packet as long as the packet mbuf is set up correctly.
-Refer to the testpmd source code (specifically the csumonly.c file) for details.
-
-That being said, the support of some offload features implies the addition of dedicated status bit(s) and value field(s) into the rte_mbuf
-data structure, along with their appropriate handling by the receive/transmit functions exported by each PMD.
-
-For instance, this is the case for the IEEE1588 packet timestamp mechanism, the VLAN tagging and the IP checksum computation, as described in
-the Section 7.6 "Meta Information".
+Also, L4 (UDP/TCP/ SCTP) checksum offload by the NIC can be enabled for an individual packet as long as the packet mbuf is set up correctly. See `Hardware Offload`_ for details.
Configuration of Transmit and Receive Queues
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When configuring for DCB operation, at port initialization, both the number of transmit queues and the number of receive queues must be set to 128.
+Hardware Offload
+~~~~~~~~~~~~~~~~
+
+Depending on driver capabilities advertised by
+``rte_eth_dev_info_get()``, the PMD may support hardware offloading
+feature like checksumming, TCP segmentation or VLAN insertion.
+
+The support of these offload features implies the addition of dedicated
+status bit(s) and value field(s) into the rte_mbuf data structure, along
+with their appropriate handling by the receive/transmit functions
+exported by each PMD. The list of flags and their precise meaning is
+described in the mbuf API documentation and in the in :ref:`Mbuf Library
+<Mbuf_Library>`, section "Meta Information".
+
Poll Mode Driver API
--------------------
~~~~~~~~~~~~~~~~~~~
The Ethernet device API exported by the Ethernet PMDs is described in the *DPDK API Reference*.
-
-Vector PMD for IXGBE
---------------------
-
-Vector PMD uses Intel® SIMD instructions to optimize packet I/O.
-It improves load/store bandwidth efficiency of L1 data cache by using a wider SSE/AVX register 1 (1).
-The wider register gives space to hold multiple packet buffers so as to save instruction number when processing bulk of packets.
-
-There is no change to PMD API. The RX/TX handler are the only two entries for vPMD packet I/O.
-They are transparently registered at runtime RX/TX execution if all condition checks pass.
-
-1. To date, only an SSE version of IX GBE vPMD is available.
- To ensure that vPMD is in the binary code, ensure that the option CONFIG_RTE_IXGBE_INC_VECTOR=y is in the configure file.
-
-Some constraints apply as pre-conditions for specific optimizations on bulk packet transfers.
-The following sections explain RX and TX constraints in the vPMD.
-
-RX Constraints
-~~~~~~~~~~~~~~
-
-Prerequisites and Pre-conditions
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-The following prerequisites apply:
-
-* To enable vPMD to work for RX, bulk allocation for Rx must be allowed.
-
-* The RTE_LIBRTE_IXGBE_RX_ALLOW_BULK_ALLOC=y configuration MACRO must be set before compiling the code.
-
-Ensure that the following pre-conditions are satisfied:
-
-* rxq->rx_free_thresh >= RTE_PMD_IXGBE_RX_MAX_BURST
-
-* rxq->rx_free_thresh < rxq->nb_rx_desc
-
-* (rxq->nb_rx_desc % rxq->rx_free_thresh) == 0
-
-* rxq->nb_rx_desc < (IXGBE_MAX_RING_DESC - RTE_PMD_IXGBE_RX_MAX_BURST)
-
-These conditions are checked in the code.
-
-Scattered packets are not supported in this mode.
-If an incoming packet is greater than the maximum acceptable length of one "mbuf" data size (by default, the size is 2 KB),
-vPMD for RX would be disabled.
-
-By default, IXGBE_MAX_RING_DESC is set to 4096 and RTE_PMD_IXGBE_RX_MAX_BURST is set to 32.
-
-Feature not Supported by RX Vector PMD
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-Some features are not supported when trying to increase the throughput in vPMD.
-They are:
-
-* IEEE1588
-
-* FDIR
-
-* Header split
-
-* RX checksum off load
-
-Other features are supported using optional MACRO configuration. They include:
-
-* HW VLAN strip
-
-* HW extend dual VLAN
-
-* Enabled by RX_OLFLAGS (RTE_IXGBE_RX_OLFLAGS_DISABLE=n)
-
-
-To guarantee the constraint, configuration flags in dev_conf.rxmode will be checked:
-
-* hw_vlan_strip
-
-* hw_vlan_extend
-
-* hw_ip_checksum
-
-* header_split
-
-* dev_conf
-
-fdir_conf->mode will also be checked.
-
-RX Burst Size
-^^^^^^^^^^^^^
-
-As vPMD is focused on high throughput, it assumes that the RX burst size is equal to or greater than 32 per burst.
-It returns zero if using nb_pkt < 32 as the expected packet number in the receive handler.
-
-TX Constraint
-~~~~~~~~~~~~~
-
-Prerequisite
-^^^^^^^^^^^^
-
-The only prerequisite is related to tx_rs_thresh.
-The tx_rs_thresh value must be greater than or equal to RTE_PMD_IXGBE_TX_MAX_BURST,
-but less or equal to RTE_IXGBE_TX_MAX_FREE_BUF_SZ.
-Consequently, by default the tx_rs_thresh value is in the range 32 to 64.
-
-Feature not Supported by RX Vector PMD
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-TX vPMD only works when txq_flags is set to IXGBE_SIMPLE_FLAGS.
-
-This means that it does not support TX multi-segment, VLAN offload and TX csum offload.
-The following MACROs are used for these three features:
-
-* ETH_TXQ_FLAGS_NOMULTSEGS
-
-* ETH_TXQ_FLAGS_NOVLANOFFL
-
-* ETH_TXQ_FLAGS_NOXSUMSCTP
-
-* ETH_TXQ_FLAGS_NOXSUMUDP
-
-* ETH_TXQ_FLAGS_NOXSUMTCP
-
-
-Sample Application Notes
-~~~~~~~~~~~~~~~~~~~~~~~~
-
-testpmd
-^^^^^^^
-
-By default, using CONFIG_RTE_IXGBE_RX_OLFLAGS_DISABLE=n:
-
-.. code-block:: console
-
- ./x86_64-native-linuxapp-gcc/app/testpmd -c 300 -n 4 -- -i --burst=32 --rxfreet=32 --mbcache=250 --txpt=32 --rxht=8 --rxwt=0 --txfreet=32 --txrst=32 --txqflags=0xf01
-
-When CONFIG_RTE_IXGBE_RX_OLFLAGS_DISABLE=y, better performance can be achieved:
-
-.. code-block:: console
-
- ./x86_64-native-linuxapp-gcc/app/testpmd -c 300 -n 4 -- -i --burst=32 --rxfreet=32 --mbcache=250 --txpt=32 --rxht=8 --rxwt=0 --txfreet=32 --txrst=32 --txqflags=0xf01 --disable-hw-vlan
-
-If scatter gather lists are not required, set CONFIG_RTE_MBUF_SCATTER_GATHER=n for better throughput.
-
-l3fwd
-^^^^^
-
-When running l3fwd with vPMD, there is one thing to note.
-In the configuration, ensure that port_conf.rxmode.hw_ip_checksum=0.
-Otherwise, by default, RX vPMD is disabled.
-
-load_balancer
-^^^^^^^^^^^^^
-
-As in the case of l3fwd, set configure port_conf.rxmode.hw_ip_checksum=0 to enable vPMD.
-In addition, for improved performance, use -bsz "(32,32),(64,64),(32,32)" in load_balancer to avoid using the default burst size of 144.
git.droids-corp.org / dpdk.git / blobdiff