[dts] TestSuite_shutdown_api.py, test_enable_disablejumbo and MTU questions

Angela Czubak aczubak at caviumnetworks.com
Wed Apr 12 19:48:00 CEST 2017


I was reading TestSuite_shutdown_api.py and have some questions about 

First of all, what are the expectations when it comes to max-pkt-len? I 
mean, self.dut.send_expect("port config all max-pkt-len %d" % 
jumbo_size, "testpmd> ") (and jumbo_size=2048) calls 
rte_eth_dev_set_mtu. How should this function interpret MTU? It believe 
it is not clearly stated, however for many drivers MTU is length of the 
IP header + its payload. Is there a DPDK convention saying otherwise? I 
mean, in send_packet_method padding is calculated subtracting both IP 
header size and ether header size. I just want to know where the border 
of dropping a packet should lie.

Secondly, why HEADER_SIZE['eth'] is equal 18? Does it take into account 
FCS? Are is there any other reason? And why rx_bytes_exp and 
tx_bytes_exp is decreased by at least 4? (send_packet method).

Last but not least, why for powerville, psringville or kawela_4 
jumbo_size is increased by 4? This happens as well in 

Thanks in advance for the response.


Angela Czubak

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