On Thu, 5 Nov 2015, Alexander V. Chernikov wrote:
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.
Ah. Thanks.
Will you make a bugzilla out of this? Or should I? Or is it not
interesting enough to fix?
/Elof
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