[Bloat] sch_fq pacing rate: Xbps, but at which layer in the network stack?

[Aaron Wood]

Eric,

Thanks for the confirmation of that.

So application pacing of say 8Mbps (1000 packets at 1000 bytes each), is
equivalent to 8.3-8.4Mbps at the interface (depending on ip header options)

So anyone planning on calling setsockopt() needs to keep that in mind? Or
is that calculated correctly for an application?

-Aaron
On Fri, Apr 14, 2017 at 11:00 Eric Dumazet <eric.dumazet at gmail.com> wrote:

> On Thu, 2017-04-13 at 20:12 -0700, Aaron Wood wrote:
> > When I was testing with my iPerf changes, I realized that the sch_fq
> > pacing (which in iperf is set via setsockopt()), is pacing at a
> > bandwidth that's set at a pretty low level in the stack (which makes
> > sense).  This is different from the application pacing that iperf does
> > (which is pacing the goodput).
> >
> >
> > But it's not clear to me where the X bps determination is being made.
> > My current guess is that it's at the interface level (since that's
> > where sch_fq is), and so it's approximately "bytes on the wire", minus
> > preambles and inter-packet spacing, and whatnot.  And so it's
> > including all the 802.x headers involved (vlan tags, qos tags,
> > source/dest macs, etc).  Is this correct?
> >
> Like other qdisc having rate limits (TBF, HTB ....), FQ sees packets
> with all headers (including Ethernet one)
>
> This is why the default quantum is 3028, which is exactly 2 regular
> Ethernet frames (MTU=1500 + 14 bytes of Ethernet header)
>
> If you have VLAN tag, it is generally not included in the calculation,
> as many devices provide 'hardware tagging'.
>
>
>
>
>
>
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