netstat -B "Recv"

[Alexander V. Chernikov]

04.11.2015, 19:55, "elof2 at sentor.se" <elof2 at sentor.se>:
> Hi!
>
> Question:
> What do the Recv column in 'netstat -B' show?
>
> I thought it was tha amount of packets received, but appaently not so.
>
> I send 2000000 packets from a tcpreplay machine to a receiving machine.
> I do it a few times.
>
> On the receiver I see:
> netstat -in
> Name Mtu Network Address Ipkts Ierrs Idrop Opkts
> Oerrs Coll
> ix0 1500 <Link#1> 0c:c4:7a:58:e2:3c 0 0 0 0
> 0 0
> ix1 1500 <Link#2> 0c:c4:7a:58:e2:3d 6000000 0 0 0
> 0 0
>
> and then
> netstat -in
> Name Mtu Network Address Ipkts Ierrs Idrop Opkts
> Oerrs Coll
> ix0 1500 <Link#1> 0c:c4:7a:58:e2:3c 0 0 0 0
> 0 0
> ix1 1500 <Link#2> 0c:c4:7a:58:e2:3d 8000000 0 0 0
> 0 0
>
> So 6000000 has increased to 8000000. Good.
>
> However, 'netstat -B' show:
>    Pid Netif Flags Recv Drop Match Sblen Hblen Command
> 25553 mon0 p--s--- 1996862 0 2000000 0 0 tcpdump
>
> How can the "Recv" be *lower* than "Match"?
> 1996862 < 2000000.
>
> For every new run (fast and slow) I get the same results, slightly less
> than 2000000 Recv.
>
> What am I missing?
Well, "Recv" is read from d->bd_rcount which is not per-cpu counter and is incrementing unlocked.
On the other hand, "Match" increases when filter returned match condition and we (w)locked bpf descriptor, so this one is accurate.

>
> /Elof
> _______________________________________________
> freebsd-net at freebsd.org mailing list
> https://lists.freebsd.org/mailman/listinfo/freebsd-net
> To unsubscribe, send any mail to "freebsd-net-unsubscribe at freebsd.org"