Thank you for your prompt reply. BCC'd Users and added dev as I believe it is the more relevant channel. I apologize for using the wrong channel initially.
I am happy to submit a patch if we would like to resolve the issue. I am confused why the hardware would have a different behavior for Rx/Tx Counters. The Tx counters do not contain the CRC bytes but the Rx counters erroneously(as you pointed out) do. I am having trouble understanding why the driver makes this discrepancy? Thank you for your time, Matt On Thu, Feb 8, 2018 at 12:32 PM, Stephen Hemminger <step...@networkplumber.org> wrote: > On Thu, 8 Feb 2018 11:52:55 -0500 > Matthew Coppola <matthew.coppo...@gmail.com> 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. > >
