[Cake] A few puzzling Cake results

[Sebastian Moeller]

> On Apr 18, 2018, at 17:03, Jonathan Morton <chromatix99 at gmail.com> wrote:
> [...]
>>> Without that, we can end up with very high drop rates which, in
>>> ingress mode, don't actually improve congestion on the bottleneck link
>>> because TCP can't reduce its window below 4 MTUs, and it's having to
>>> retransmit all the lost packets as well.  That loses us a lot of
>>> goodput for no good reason.
>> 
>> I can sorta, maybe, see the point of not dropping packets that won't
>> cause the flow to decrease its rate *in ingress mode*. But this is also
>> enabled in egress mode, where it doesn't make sense.
> 
> I couldn't think of a good reason to switch it off in egress mode.  That would improve a metric that few people care about or can even measure, while severely increasing packet loss and retransmissions in some situations, which is something that people *do* care about and measure.
[...]

Just a thought, in egress mode in the typical deployment we expect, the bandwidth leading into cake will be >> than the bandwidth out of cake, so I would argue that the package droppage might be acceptable on egress as there is bandwidth to "waste" while on ingress the issue very much is that all packets cake sees already used up parts of the limited transfer time on the bottleneck link and hence are more "precious", no? Users wanting this new behavior could still use the ingress keyword even on egress interfaces?

Best Regards
	Sebastian