92. MTU Check Tests

The support of jumbo frames by Poll Mode Drivers consists in enabling a port to receive Jumbo Frames with a configurable maximum packet length that is greater than the standard maximum Ethernet frame length (1518 bytes), up to a maximum value imposed by the hardware.

Note

Maximum Packet Length = MTU(Maximum Transmission Unit) + 14(src mac + dst mac + LEN/TYPE) + 4(CRC) e.g., 1518 = 1500 + 14 + 4

92.1. Prerequisites

If using vfio the kernel must be >= 3.6+ and VT-d must be enabled in bios.When using vfio, use the following commands to load the vfio driver and bind it to the device under test:

modprobe vfio
modprobe vfio-pci
usertools/dpdk-devbind.py --bind=vfio-pci device_bus_id

Assuming that ports 0 and 1 of the test target are directly connected to the traffic generator, launch the testpmd application with the following arguments:

./build/app/testpmd -c ffffff -n 6 -- -i --portmask=0x3 --max-pkt-len=9600 \
--tx-offloads=0x00008000

The -n command is used to select the number of memory channels. It should match the number of memory channels on that setup.

Setting tx-offload to 0x8000 and the maximum packet length to 9600 (CRC included) makes input Jumbo Frames to be stored in multiple buffers by the hardware RX engine.

Start packet forwarding in the testpmd application with the start command.

92.2. Functional Tests of MTU Checks

Testing the support of MTU Size Checks in Poll Mode Drivers consists of configuring the MTU to a given value, and then checking that DPDK registers the change in MTU size. Then, a packet is sent that is the size of the MTU, validating that no error was produced. A packet is then sent which is larger than the MTU by 100 bytes, validating that an error is produced. All tests are identical, ignoring the change in MTU and packet size. As such, only 1 test case has been included for brevity. The sized given below are the size of the IP header and the payload of the IP Packet. Each test will set the MTU to that value, then send 1 packet of exactly that size that should work properly. Then, the test will send a packet that is 100 bytes larger than the MTU, which should not be received.

  1. MTU = 1500
  2. MTU = 2400
  3. MTU = 4800
  4. MTU = 9000

92.3. Test Case: MTU of 1500

Stop all ports:

testpmd> port stop all
Stopping ports...
Checking link statuses...
Done

Set MTU size to 1500

testpmd> port config mtu 0 1500
testpmd> port config mtu 1 1500

Restart the ports

testpmd> port start all
Port 0: 3C:FD:FE:B2:AC:F8
Port 1: 3C:FD:FE:B2:AC:F9
Port 2: 3C:FD:FE:B2:AC:FA
Port 3: 3C:FD:FE:B2:AC:FB
Checking link statuses...
Done

Send a packet with size 1500 bytes

testpmd> show port stats 0
  ######################## NIC statistics for port 0  ########################
  RX-packets: 0          RX-errors: 0         RX-bytes: 0
  TX-packets: 1          TX-errors: 0         TX-bytes: 1500
  ############################################################################

testpmd> show port stats 1

  ######################## NIC statistics for port 1  ########################
  RX-packets: 1          RX-errors: 0         RX-bytes: 1500
  TX-packets: 0          TX-errors: 0         TX-bytes: 0
  ############################################################################

Verify that TX-bytes on port 0 and RX-bytes on port 1 are 1500

Send a packet with size 1600 bytes

testpmd> show port stats 0

  ######################## NIC statistics for port 0  ########################
  RX-packets: 0          RX-errors: 0         RX-bytes: 0
  TX-packets: 1          TX-errors: 0         TX-bytes: 1500
  ############################################################################

testpmd> show port stats 1

  ######################## NIC statistics for port 1  ########################
  RX-packets: 1          RX-errors: 0         RX-bytes: 1500
  TX-packets: 0          TX-errors: 0         TX-bytes: 0
  ############################################################################

Verify that TX-bytes on port 0 and RX-bytes on port 1 are 1500