[Cake] More on 'target' corner cases - rate/target/interval confusion?

Toke Høiland-Jørgensen toke at toke.dk
Tue Nov 3 08:56:52 EST 2015

Sebastian Moeller <moeller0 at gmx.de> writes:

> I thought the rationale was that a target be tow the transfer time for
> a single MTU packet is not too reasonable as the queue will enter
> dropping state for each (full MTU) packet transferred.

Yes, that is exactly it. But that happens when the packet at the head of
the queue is waiting on the packet *before* it, which will be in a lower
layer in the process of being transferred (at low bandwidths that "lower
layer" has in practice been HTB).

However, now that cake itself is doing the delaying (via the packet
transmission scheduling), this is not as clear-cut. The actual packet at
the head of the queue is now the one being delayed. I'm afraid I don't
quite grok how the shaper and CoDel interacts in this case; guess I'll
go read the code.

> I guess most VoIP packets will not be full MTU, so on a dedicated VoIP
> queue the 1.5 * full MTU idea might be sub-optimal...

That is also a (separate IMO) issue; however, as Dave said, we need to
be vary of just assuming that the VoIP queue will be only small VoIP
packets: there's no admission control!


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