netstat -i not accurate on -stable ?

[Olivier Cochard-Labbé]

Hi all,

I was testing my pthread-netblbast (PR bin/179085) when I found a
problem with netstat counters (tested on 9-stable r252056).

netreceive (src/toots/tools/netrate) display this output:
    542025 pps   43.362 Mbps - 271554 pkts in 0.500998393 ns
    541562 pps   43.325 Mbps - 271323 pkts in 0.501000754 ns
    541517 pps   43.321 Mbps - 271300 pkts in 0.500999700 ns
    540487 pps   43.239 Mbps - 270784 pkts in 0.500999904 ns
    541541 pps   43.323 Mbps - 271312 pkts in 0.500999621 ns
    540624 pps   43.250 Mbps - 270853 pkts in 0.501000361 ns
    541403 pps   43.312 Mbps - 271243 pkts in 0.500999669 ns
    541079 pps   43.286 Mbps - 271081 pkts in 0.501000212 ns
    540887 pps   43.271 Mbps - 270985 pkts in 0.501000258 ns
    541796 pps   43.344 Mbps - 271440 pkts in 0.500999971 ns
    541056 pps   43.284 Mbps - 271069 pkts in 0.500999719 ns
    541224 pps   43.298 Mbps - 271155 pkts in 0.501002856 ns
    541120 pps   43.290 Mbps - 271100 pkts in 0.500997659 ns

But in the same time a "netstat -ihw 1" display this output:
            input        (Total)           output
   packets  errs idrops      bytes    packets  errs      bytes colls
      521k  508k     0        30M          3     0        562     0
      521k  511k     0        30M          3     0        514     0
      521k  526k     0        30M          3     0        514     0
      521k  538k     0        30M          4     0        616     0
      521k  495k     0        30M          3     0        514     0
      521k  502k     0        30M          3     0        514     0
      521k  531k     0        30M          3     0        514     0
      521k  502k     0        30M          3     0        514     0
      521k  504k     0        30M          3     0        514     0
      521k  495k     0        30M          3     0        514     0
      521k  498k     0        30M          3     0        514     0
      521k  516k     0        30M          3     0        514     0

There are about 20Kpps difference between them.

Regards,

Olivier