04.11.2015, 19:55, "el...@sentor.se" <el...@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.
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