On Thu, 8 Feb 2018 11:52:55 -0500 Matthew Coppola <[email protected]> wrote:
> 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. It is an Intel driver bug. All drivers must NOT include CRC bytes in counters. The DPDK (and Linux, BSD) convention is that byte counters do not include the CRC bytes. Note: Cisco routers include the CRC bytes; but everyone else does not.
