On Sat, 29 Dec 2012 18:31:56 -0800
Eric Dumazet [off-list ref] wrote:

On Sat, 2012-12-29 at 23:44 -0200, Flavio Leitner wrote:

quoted

Speaking as a support engineer, it's a lot easier to grab ethtool -S and
see everything than grab two or more outputs.

I agree its very convenient.

I have a patch to add GRO statistics at the core layer, in the ethtool
-S stats. 

I was about to ask netdev guys what they think of this idea ?


net-gro: Add GRO counters to ethtool -S
    
In order to get an idea of how effective is GRO aggregation on a machine,
we need appropriate counters. Preferably use "ethtool -S" to display them
on a per device basis, or even per RX queue.
    
In this implementation, I chose to not change NIC drivers.

Core network stack adds the gro counters at the end of the counters
each NIC driver provides for ethtool -S
    
There are 5 counters per RX queue :
    
    gro_complete:  number of time the NAPI handler did not consume its budget
                   (This force a flush of all GRO packets in the GRO queue)
    gro_overflows: number of time a segment could not be stored in GRO queue
                   because current number or messages is too high
    gro_nogro:     number of time a segment was not stored in GRO queue.
                   (Because its not a TCP packet, or it includes a
                   SYN/FIN/RST/PSH flag)
    gro_msgs:      number of GRO messages (might contain 1 to 17 segments)
    gro_segs:      number of GRO segments
    
Example:
    
     On receiver machine, with 8 RX queues :

     ethtool -S eth4 | tail -n 10
         gro_complete[7]: 56635
         gro_overflows[7]: 0
         gro_nogro[7]: 212
         gro_msgs[7]: 129410
         gro_segs[7]: 1434925
         gro_complete: 699479
         gro_overflows: 0
         gro_nogro: 2455
         gro_msgs: 1626470
         gro_segs: 17876794
    
    In this example, we can compute average number of segments per GRO message :
    
    17876794/17876794 = 10.99
    
    Or more precisely : 17876794/(17876794+2455) = 10.97


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Ethtool is awkward because it is only available through ioctl, no netlink or /proc.
If you use ethtool for GRO, please make it a separate ioctl not an add-on to
existing device statistics.  ethtool --gro ??