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Subject: Re: netstat -B "Recv" 
From: Christian Peron <csjp@sqrt.ca>
In-Reply-To: <alpine.BSF.2.00.1511051518330.49057@farmermaggot.shire.sentor.se>
Date: Fri, 6 Nov 2015 14:22:29 -0600
Cc: "Alexander V. Chernikov" <melifaro@freebsd.org>,
 freebsd-net <freebsd-net@freebsd.org>
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To: elof2@sentor.se
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It needs to get fixed.. let me generate a patch for you and you can test =
it.


> On Nov 5, 2015, at 8:51 AM, elof2@sentor.se wrote:
>=20
> On Thu, 5 Nov 2015, Alexander V. Chernikov wrote:
>=20
>>=20
>>=20
>> 04.11.2015, 19:55, "elof2@sentor.se" <elof2@sentor.se>:
>>> Hi!
>>>=20
>>> Question:
>>> What do the Recv column in 'netstat -B' show?
>>>=20
>>> I thought it was tha amount of packets received, but appaently not =
so.
>>>=20
>>> I send 2000000 packets from a tcpreplay machine to a receiving =
machine.
>>> I do it a few times.
>>>=20
>>> 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
>>>=20
>>> 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
>>>=20
>>> So 6000000 has increased to 8000000. Good.
>>>=20
>>> However, 'netstat -B' show:
>>>    Pid Netif Flags Recv Drop Match Sblen Hblen Command
>>> 25553 mon0 p--s--- 1996862 0 2000000 0 0 tcpdump
>>>=20
>>> How can the "Recv" be *lower* than "Match"?
>>> 1996862 < 2000000.
>>>=20
>>> For every new run (fast and slow) I get the same results, slightly =
less
>>> than 2000000 Recv.
>>>=20
>>> 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.
>=20
> Ah. Thanks.
>=20
>=20
> Will you make a bugzilla out of this? Or should I? Or is it not =
interesting enough to fix?
>=20
> /Elof
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