netdev - Re: [PATCH net-next] add part of TCP counts explanations in snmp

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Date:   Mon, 19 Nov 2018 19:10:02 -0800
From:   peng yu <yupeng0921@...il.com>
To:     stephen@...workplumber.org
Cc:     netdev@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>,
        rdunlap@...radead.org
Subject: Re: [PATCH net-next] add part of TCP counts explanations in snmp_counters.rst

On Mon, Nov 19, 2018 at 10:51 AM Stephen Hemminger
<stephen@...workplumber.org> wrote:
>
> On Fri, 16 Nov 2018 11:17:40 -0800
> yupeng <yupeng0921@...il.com> wrote:
>
> > +* TcpInSegs
> > +Defined in `RFC1213 tcpInSegs`_
> > +
> > +.. _RFC1213 tcpInSegs: https://tools.ietf.org/html/rfc1213#page-48
> > +
> > +The number of packets received by the TCP layer. As mentioned in
> > +RFC1213, it includes the packets received in error, such as checksum
> > +error, invalid TCP header and so on. Only one error won't be included:
> > +if the layer 2 destination address is not the NIC's layer 2
> > +address. It might happen if the packet is a multicast or broadcast
> > +packet, or the NIC is in promiscuous mode. In these situations, the
> > +packets would be delivered to the TCP layer, but the TCP layer will discard
> > +these packets before increasing TcpInSegs. The TcpInSegs counter
> > +isn't aware of GRO. So if two packets are merged by GRO, the TcpInSegs
> > +counter would only increase 1.
>
> Is it it obvious that TCP which is L4 masks off all the other things
> that could happen at L3 and L2.  SO this text is correct but redundant.

You mentioned the text is redundant, I'm not sure which part you are
talking about.
If you are talking about the GRO part, here is my explanation: the
TcpInSegs isn't aware of GRO, but TcpOutSegs is aware of GSO, when
server A sends packets to server B, the TcpOutSegs on server A might
be much higher than the TcpInSegs on server B, so I think it is worth
to point it out.
If you are talking about the other part, please let me know.