[dpdk-dev] ixgbe: account more Rx errors Issue

[Tahhan, Maryam]

> From: Andriy Berestovskyy [mailto:aber at semihalf.com]
> Sent: Friday, September 4, 2015 5:59 PM
> To: Tahhan, Maryam
> Cc: dev at dpdk.org; Olivier MATZ
> Subject: Re: ixgbe: account more Rx errors Issue
> 
> Hi Maryam,
> Please see below.
> 
> > XEC counts the Number of receive IPv4, TCP, UDP or SCTP XSUM errors
> 
> Please note than UDP checksum is optional for IPv4, but UDP packets with
> zero checksum hit XEC.
> 

I understand, but this is what the hardware register is picking up and what I included previously is the definitions of the registers from the datasheet.

> > And general crc errors counts Counts the number of receive packets with
> CRC errors.
> 
> Let me explain you with an example.
> 
> DPDK 2.0 behavior:
> host A sends 10M IPv4 UDP packets (no checksum) to host B host B stats: 9M
> ipackets + 1M ierrors (missed) = 10M
> 
> DPDK 2.1 behavior:
> host A sends 10M IPv4 UDP packets (no checksum) to host B host B stats: 9M
> ipackets + 11M in ierrors (1M missed + 10M XEC) = 20M?

Because it's hitting the 2 error registers. If you had packets with multiple errors that are added up as part of ierrors you'll still be getting more than 10M errors which is why I asked for feedback on the 3 suggestions below. What I'm saying is the number of errors being > the number of received packets will be seen if you hit multiple error registers on the NIC.

> 
> > So our options are we can:
> > 1. Add only one of these into the error stats.
> > 2. We can introduce some cooking of stats in this scenario, so only add
> either or if they are equal or one is higher than the other.
> > 3. Add them all which means you can have more errors than the number of
> received packets, but TBH this is going to be the case if your packets have
> multiple errors anyway.
> 
> 4. ierrors should reflect NIC drops only.

I may have misinterpreted this, but ierrors in rte_ethdev.h ierrors is defined as the Total number of erroneous received packets.
Maybe we need a clear definition or a separate drop counter as I see uint64_t q_errors defined as: Total number of queue packets received that are dropped.

> XEC does not count drops, so IMO it should be removed from ierrors.

While it's picking up the 0 checksum as an error (which it shouldn't necessarily be doing), removing it could mean missing other valid L3/L4 checksum errors... Let me experiment some more with L3/L4 checksum errors and crcerrs to see if we can cook the stats around this register in particular. I would hate to remove it and miss genuine errors 

> 
> Please note that we still can access the XEC using rte_eth_xstats_get()
> 
> 
> Regards,
> Andriy