Re: ixgbe: account more Rx errors Issue

[Olivier MATZ <olivier.matz@6wind.com>]

Hi,

On 09/06/2015 07:15 PM, Tahhan, Maryam wrote:
>> From: Andriy Berestovskyy [mailto:aber@semihalf.com]
>> Sent: Friday, September 4, 2015 5:59 PM
>> To: Tahhan, Maryam
>> Cc: dev@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



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