Description of problem:
As per https://www.rfc-editor.org/rfc/rfc2819.html stats for packet size are reported "including FCS".

However in DPDK vhost the packet size is being reported without an FCS which leads to a 4 byte offset in stat value. This means that packets near a boundary may be counted in the wrong packet size bucket.

It also means that for a PVP test using 64 byte packets from the traffic gen, the packets are being reported from vhost as 60 byte packets which increments the undersize pkts counters that is then reported in OVS stats.

This issue reported in https://bugzilla.redhat.com/show_bug.cgi?id=2175079#c10

Version-Release number of selected component (if applicable):
DPDK 22.11 (OVS 3.1)

Steps to Reproduce:
1. Setup PVP test with 64 byte packets
2. Check OVS vhost stats for undersize packets

=====================================

 
mcoqueli@redhat.com added a comment - 2023/04/19 8:57 AM - Restricted to Red Hat Bugzilla Authorized
Created attachment 1958236 [details]
Vhost: Add FCS size for RFC 2819 compliance

I have implemented this DPDK Vhost library patch that adds the FCS size before
adding to the VQ total bytes and distributing the packets into the sizes buckets.

Doing this, we would be compliant with RFC 2819, but we create another problem in OVS.
Indeed, the VQ total bytes counters are summed to form the Vhost port total bytes counter, which used to not account for the FCS size.