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

[Eric Dumazet]

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'.