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37 Vector PMD uses IntelĀ® SIMD instructions to optimize packet I/O.
38 It improves load/store bandwidth efficiency of L1 data cache by using a wider SSE/AVX register 1 (1).
39 The wider register gives space to hold multiple packet buffers so as to save instruction number when processing bulk of packets.
41 There is no change to PMD API. The RX/TX handler are the only two entries for vPMD packet I/O.
42 They are transparently registered at runtime RX/TX execution if all condition checks pass.
44 1. To date, only an SSE version of IX GBE vPMD is available.
45 To ensure that vPMD is in the binary code, ensure that the option CONFIG_RTE_IXGBE_INC_VECTOR=y is in the configure file.
47 Some constraints apply as pre-conditions for specific optimizations on bulk packet transfers.
48 The following sections explain RX and TX constraints in the vPMD.
53 Prerequisites and Pre-conditions
54 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
56 The following prerequisites apply:
58 * To enable vPMD to work for RX, bulk allocation for Rx must be allowed.
60 * The RTE_LIBRTE_IXGBE_RX_ALLOW_BULK_ALLOC=y configuration MACRO must be set before compiling the code.
62 Ensure that the following pre-conditions are satisfied:
64 * rxq->rx_free_thresh >= RTE_PMD_IXGBE_RX_MAX_BURST
66 * rxq->rx_free_thresh < rxq->nb_rx_desc
68 * (rxq->nb_rx_desc % rxq->rx_free_thresh) == 0
70 * rxq->nb_rx_desc < (IXGBE_MAX_RING_DESC - RTE_PMD_IXGBE_RX_MAX_BURST)
72 These conditions are checked in the code.
74 Scattered packets are not supported in this mode.
75 If an incoming packet is greater than the maximum acceptable length of one "mbuf" data size (by default, the size is 2 KB),
76 vPMD for RX would be disabled.
78 By default, IXGBE_MAX_RING_DESC is set to 4096 and RTE_PMD_IXGBE_RX_MAX_BURST is set to 32.
80 Feature not Supported by RX Vector PMD
81 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
83 Some features are not supported when trying to increase the throughput in vPMD.
92 * RX checksum off load
94 Other features are supported using optional MACRO configuration. They include:
100 * Enabled by RX_OLFLAGS (RTE_IXGBE_RX_OLFLAGS_DISABLE=n)
103 To guarantee the constraint, configuration flags in dev_conf.rxmode will be checked:
115 fdir_conf->mode will also be checked.
120 As vPMD is focused on high throughput, it assumes that the RX burst size is equal to or greater than 32 per burst.
121 It returns zero if using nb_pkt < 32 as the expected packet number in the receive handler.
129 The only prerequisite is related to tx_rs_thresh.
130 The tx_rs_thresh value must be greater than or equal to RTE_PMD_IXGBE_TX_MAX_BURST,
131 but less or equal to RTE_IXGBE_TX_MAX_FREE_BUF_SZ.
132 Consequently, by default the tx_rs_thresh value is in the range 32 to 64.
134 Feature not Supported by RX Vector PMD
135 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
137 TX vPMD only works when txq_flags is set to IXGBE_SIMPLE_FLAGS.
139 This means that it does not support TX multi-segment, VLAN offload and TX csum offload.
140 The following MACROs are used for these three features:
142 * ETH_TXQ_FLAGS_NOMULTSEGS
144 * ETH_TXQ_FLAGS_NOVLANOFFL
146 * ETH_TXQ_FLAGS_NOXSUMSCTP
148 * ETH_TXQ_FLAGS_NOXSUMUDP
150 * ETH_TXQ_FLAGS_NOXSUMTCP
153 Sample Application Notes
154 ~~~~~~~~~~~~~~~~~~~~~~~~
159 By default, using CONFIG_RTE_IXGBE_RX_OLFLAGS_DISABLE=n:
161 .. code-block:: console
163 ./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
165 When CONFIG_RTE_IXGBE_RX_OLFLAGS_DISABLE=y, better performance can be achieved:
167 .. code-block:: console
169 ./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
174 When running l3fwd with vPMD, there is one thing to note.
175 In the configuration, ensure that port_conf.rxmode.hw_ip_checksum=0.
176 Otherwise, by default, RX vPMD is disabled.
181 As in the case of l3fwd, set configure port_conf.rxmode.hw_ip_checksum=0 to enable vPMD.
182 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.