[Cake] Long-RTT broken again

Toke Høiland-Jørgensen toke at toke.dk
Tue Nov 3 06:50:38 EST 2015

Jonathan Morton <chromatix99 at gmail.com> writes:

>> On 2 Nov, 2015, at 20:29, Sebastian Moeller <moeller0 at gmx.de> wrote:
>> the initial commit was not as well tested as it should have been…
> Indeed, and the obvious problems with it were why I reverted it.  I
> was able to put in a partial implementation by other means at the same
> time, but haven’t yet had time to polish off the rough edges.

Well I would have preferred that you kept the part that fixed the (real,
demonstrated) bug, and then went back and fixed the (theoretical) memory
limit issues later; which I was well aware were there.

And BTW, I'm not entirely convinced that this is anything but a
theoretical problem; I challenge anyone to actually demonstrate a router
crashing from OOM from this. :)

> The question remains why a 15MB buffer (which comfortably exceeds the
> traditional FIFO rule of thumb for 1 second * 100Mbps) is apparently
> insufficient according to Toke’s tests, even with the target increased
> as requested.

Because it's not a 15MB buffer; it's a 10240 packet buffer. So anything
from ~.5 to ~15MB. In this case, it's a bidirectional test, so about
half the packets will be tiny ACKs. I guess doing byte accounting would
actually be better here, regardless of what happens to the overall limit... :)


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