[dts] TestSuite_shutdown_api.py, test_enable_disablejumbo and MTU questions
Angela Czubak
aczubak at caviumnetworks.com
Thu Apr 13 18:08:38 CEST 2017
Ok, partially answering to myself: max-pkt-len is different than MTU,
there is no call to rte_eth_dev_set_mtu when calling "port config all
max-pkt-len". It is truly setting max_rx_pkt_len of
port->dev_conf.rxmode in init_port_config (and then the device is
reconfigured with rte_eth_dev_configure when starting the port).
This somehow explains, that decreasing by 4 in send_packet might be
connected to the fact that NIC may or may not take FCS into frame length.
So now I only don't know why HEADER_SIZE['eth'] is 18 (for sure) and why
powerville, springville and kawela_4 are treated differently.
On 12.04.2017 19:48, Angela Czubak wrote:
> Hi,
>
>
> I was reading TestSuite_shutdown_api.py and have some questions about
> test_enable_disablejumbo.
>
> 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
> test_enable_disablejumbo.
>
> Thanks in advance for the response.
>
>
> Regards,
>
> Angela Czubak
>
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