[Cake] [Ecn-sane] l4s kernel submission

Dave Taht dave.taht at gmail.com
Tue Oct 19 10:16:52 EDT 2021

On Tue, Oct 19, 2021 at 6:34 AM Sebastian Moeller <moeller0 at gmx.de> wrote:
> So that still leaves us with GSO introducing CE "spikes" into the network, that might not necessarily reflect what would happened if the meta-packet had been segmented before....

I am not sure the proper term for this, the "wavefront" of a GSO'd
packet will get scheduled and not marked, and the tail of the wave,
were it not GSO'd, might be marked. The next wavefront, assuming it's
accumulated a negative deficit, will all be marked. Now what this
means for the next "wavefront" I don't really understand, my guess is
packets will start to get paced naturally from the sender but might
still be arriving in a bunch to the receiver.

On the GRO side, I am glad toke has reassured me that at least in
linux, GRO checks all the headers. as for what hardware offloads or
the device drivers might do, unknown.

In our world we've been splitting up gro/gso in self defense so much
that we don't know what the rest of the world looks like. sch_fq has a
3000 byte quantum and always releases two packets by default.

> I note that rfc3168 probably will not care, since it will signal a CE mark for >= a full RTT anyway, but HFCCs will care.

I have long thought that responding better to multiple rfc3168 marks
in an RTT would be a nice addition for a transport to have. But, no,
they don't care.

> Regards
>         Sebastian
> > On Oct 19, 2021, at 15:30, Dave Taht <dave.taht at gmail.com> wrote:
> >
> > On Tue, Oct 19, 2021 at 4:19 AM Toke Høiland-Jørgensen <toke at toke.dk> wrote:
> >>
> >> Dave Taht <dave.taht at gmail.com> writes:
> >>
> >>> my more specific question was gro. On gro assembly is the dscp/ecn
> >>> header examined?
> >>
> >> Yes, and only packets with the same value get aggregated:
> >> https://elixir.bootlin.com/linux/latest/source/net/ipv6/ip6_offload.c#L263
> >
> > Good to know. Thx.
> >
> >> -Toke
> >
> >
> >
> > --
> > Fixing Starlink's Latencies: https://www.youtube.com/watch?v=c9gLo6Xrwgw
> >
> > Dave Täht CEO, TekLibre, LLC

Fixing Starlink's Latencies: https://www.youtube.com/watch?v=c9gLo6Xrwgw

Dave Täht CEO, TekLibre, LLC

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