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

[Tahhan, Maryam]

> From: Olivier MATZ [mailto:olivier.matz at 6wind.com]
> Sent: Monday, September 7, 2015 9:30 AM
> To: Tahhan, Maryam; Andriy Berestovskyy
> Cc: dev at dpdk.org
> Subject: Re: ixgbe: account more Rx errors Issue
> 
> Hi,
> 
> On 09/06/2015 07:15 PM, Tahhan, Maryam wrote:
> >> 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
> 
> For me, the definition that looks the most straightforward is:
> 
> ipackets = packets successfully received by hardware imissed = packets
> dropped by hardware because the software does
>   not poll fast enough (= queue full)
> ierrors = packets dropped by hardware (malformed packets, ...)
> 
> These 3 stats never count twice the same packet.
> 
> If we want more statistics, they could go in xstats. For instance, a counter for
> invalid checksum. The definition of these stats would be pmd-specific.
> 
> I agree we should clarify and have a consensus on the definitions before going
> further.
> 
> 
> Regards,
> Olivier

Hi Olivier
I think it's important to distinguish between errors and drops and provide a statistics API that exposes both. This way people have access to as much information as possible when things do go wrong and nothing is missed in terms of errors.

My suggestion for the high level registers would be:
ipackets = Total number of packets successfully received by hardware
imissed = Total number of  packets dropped by hardware because the software does not poll fast enough (= queue full)
idrops = Total number of packets dropped by hardware (malformed packets, ...) Where the # of drops can ONLY be <=  the packets received (without overlap between registers).
ierrors = Total number of erroneous received packets. Where the # of errors can be >= the packets received (without overlap between registers), this is because there may be multiple errors associated with a packet.

This way people can see how many packets were dropped and why at a high level as well as through the extended stats API rather than using one API or the other. What do you think?

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