[Cake] Long-RTT broken again

Toke Høiland-Jørgensen toke at toke.dk
Sat Nov 7 03:48:58 EST 2015

Jonathan Morton <chromatix99 at gmail.com> writes:

>> On 6 Nov, 2015, at 16:15, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>> Added a run with Reno to the same directory. Smoother, but worse overall
>> throughput.
> Yes, looks like it’s ramping up the slow way, and hasn’t reached the
> BDP by the time the test run ended.
> However, it also looks like it’s properly ack-clocked, unlike CUBIC,
> so while it’s still bursty, it isn’t overflowing the buffer except
> during slow-start.

Hmm, right. Can run a longer test to see if it ever reaches 100Mbit; and
also add in a BIFO queue for comparison.

> The fact that slow-start terminates (due to loss) after only a few
> RTTs is suspicious.  What parameters are you giving to netem?  I note
> that the default packet limit in netem is 1000, which is 1.5MB...

Not using netem - don't trust it. The delay is added by dummynet which
is on a separate box in the middle. And dummynet basically has an
infinite buffer; no packets are dropped there (yes, I checked) :)


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