[Bloat] Apple WWDC Talks on Latency/Bufferbloat

[Matt Mathis]

Which WG are you targeting?

Thanks,
--MM--
The best way to predict the future is to create it.  - Alan Kay

We must not tolerate intolerance;
       however our response must be carefully measured:
            too strong would be hypocritical and risks spiraling out of
control;
            too weak risks being mistaken for tacit approval.


On Thu, Jun 17, 2021 at 4:43 PM Christoph Paasch <cpaasch at apple.com> wrote:

> Hello,
>
> On 06/17/21 - 11:16, Matt Mathis via Bloat wrote:
> > Is there a paper or spec for RPM?
>
> we try to publish an IETF-draft on the methodology before the upcoming IETF
> in July.
>
> But, in the mean-time please see inline:
>
> > There are at least two different ways to define RPM, both of which might
> be
> > relevant.
> >
> > At the TCP layer: it can be directly computed from a packet capture.  The
> > trick is to time reverse a trace and compute the critical path backwards
> > through the trace: what event triggered each segment or ACK, and count
> > round trips.  This would be super robust but does not include the
> queueing
> > required in the kernel socket buffers.  I need to think some more about
> > computing TCP RPM from tcp_info or other kernel instrumentation - it
> might
> > be possible.
>
> We explicitly opted against measuring purely TCP-level round-trip times.
> Because
> there are countless transparent TCP-proxies out there that would skew these
> numbers. Our goal with RPM/Responsiveness is to measure how an end-user
> would
> experience the network. Which means, DNS-resolution, TCP handshake-time,
> TLS-handshake, HTTP/2 Request/response. Because, at the end, that's what
> actually matters to the users.
>
> > A different RPM can be done in the application, above TCP, for example by
> > ping-ponging messages.  This would include the delays traversing the
> kernel
> > socket buffers which have to be at least as large as a full network RTT.
> >
> > This is perhaps an important point: due to the retransmit and
> > reassuebly queues (which are required to implement robust data delivery)
> > TCP must be able hold at least a full RTT of data in it's own buffers,
> > which means that under some conditions the RTT as seen by the application
> > has be be at least twice the network's RTT, including any bloat in the
> > network.
>
> Currently, we measure RPM on separate connections (not the load-bearing
> ones). We are also measuring on the load-bearing connections themselves
> through H2 Ping frames. But for the reasons you described we haven't yet
> factored it into the RPM-number.
>
> One way may be to inspect with TCP_INFO whether or not the connections had
> retransmissions and then throw away the number. On the other hand, if the
> network becomes extremely lossy under working conditions, it does impact
> the
> user-experience and so it could make sense to take this into account.
>
>
> In the end, we realized how hard it is to accurately measure bufferbloat
> within a reasonable time-frame (our goal is to finish the test within ~15
> seconds).
>
> We hope that with the IETF-draft we can get the right people together to
> iterate over it and squash out a very accurate measurement that represents
> what users would experience.
>
>
> Cheers,
> Christoph
>
>
> >
> > Thanks,
> > --MM--
> > The best way to predict the future is to create it.  - Alan Kay
> >
> > We must not tolerate intolerance;
> >        however our response must be carefully measured:
> >             too strong would be hypocritical and risks spiraling out of
> > control;
> >             too weak risks being mistaken for tacit approval.
> >
> >
> > On Sat, Jun 12, 2021 at 9:11 AM Rich Brown <richb.hanover at gmail.com>
> wrote:
> >
> > > > On Jun 12, 2021, at 12:00 PM, bloat-request at lists.bufferbloat.net
> wrote:
> > > >
> > > > Some relevant talks / publicity at WWDC -- the first mentioning
> CoDel,
> > > > queueing, etc. Featuring Stuart Cheshire. iOS 15 adds a developer
> test
> > > for
> > > > loaded latency, reported in "RPM" or round-trips per minute.
> > > >
> > > > I ran it on my machine:
> > > > nowens at mac1015 ~ % /usr/bin/networkQuality
> > > > ==== SUMMARY ====
> > > > Upload capacity: 90.867 Mbps
> > > > Download capacity: 93.616 Mbps
> > > > Upload flows: 16
> > > > Download flows: 20
> > > > Responsiveness: Medium (840 RPM)
> > >
> > > Does anyone know how to get the command-line version for current (not
> > > upcoming) macOS? Thanks.
> > >
> > > Rich
> > > _______________________________________________
> > > Bloat mailing list
> > > Bloat at lists.bufferbloat.net
> > > https://lists.bufferbloat.net/listinfo/bloat
> > >
>
> > _______________________________________________
> > Bloat mailing list
> > Bloat at lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/bloat
>
>
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