Hi, I am noticing a discrepancy in the Rx/Tx Byte counters when using the i40e driver as a virtual function. Specifically I am observing that the Rx bytes are 4 bytes per packet larger than the Tx Bytes.
My application is transmitting a packet and then receiving the same packet back (in a service function chaining application). I verified that the packets being transmitted and received were the same by capturing on the interfaces using pdump and analyzing the output in Wireshark. I believe the discrepancy comes from correcting for the Ethernet FCS. I see that in i40e_ethdev.c the CRC bytes are corrected for in the i40e_update_vsi_stats() and i40e_read_stats_registers() functions by using the following correction (see below). Note the left-hand side changes slightly depending on the specific function. pf->internal_stats.rx_bytes -= (pf->internal_stats.rx_unicast + pf->internal_stats.rx_multicast + pf->internal_stats.rx_broadcast) * ETHER_CRC_LEN; However I did not see this correction being used in the vf driver (i40e_ethdev_vf.c). By adding a correction to i40evf_update_stats() as follows I can reconcile the counters (and make them consistent with the PF behavior). nes->rx_bytes -= (nes->rx_unicast + nes->rx_multicast + nes->rx_broadcast) * ETHER_CRC_LEN; I would like to know if this is the expected behavior or if this is a bug in the driver? If this is the expected behavior can you please explain why I should expect a discrepancy between the Rx and Tx Byte counters? Some additional information: The application I am observing this behaviour in is using DPDK 17.08. (However I don't see any fixes for this in version 17.11). The NIC is an Intel Corporation XL710/X710 Virtual Function (rev 02) (output from lspci). Thank you for your time, and please let me know if you require further information. Matt m
