> On Sep 7, 2018, at 1:03 AM, Jonathan Morton <chromati...@gmail.com> wrote:
>
>> On 7 Sep, 2018, at 1:37 am, Pete Heist <p...@heistp.net> wrote:
>>
>> This router is an old ALIX with kernel 2.6.26, but on the other hand it does
>> have hfsc + esfq (a variant of sfq with host fairness) deployed, so if it’s
>> actually controlling the queue, one might suspect that sfq it could control
>> inter-flow latency at least somewhat.
>
> ESFQ has two important faults: it doesn't explicitly control the length of
> individual queues (only tail-drops when a global limit is reached), and it
> suffers from hash collisions at the full "birthday problem" rate. So some of
> your measurement traffic is likely colliding with real traffic and suffering
> accordingly.
Ah, ok, that is important.
> That still makes ESFQ far better than a dumb FIFO.
I’ve heard tales of the way things were.
As a contrast, the router I’m on:
https://www.heistp.net/downloads/vysina_ping.pdf
<https://www.heistp.net/downloads/vysina_ping.pdf> The big difference here is
this router’s uplink is licensed spectrum full-duplex 100Mbit, whereas Jerab
from earlier is 5GHz WiFi (2x NSM5). The shift around June was an upgrade from
ALIX to APU.
I haven’t seen evidence yet of backhaul links running at saturation for long
periods. When I watch throughputs in real-time I do see pulses though that
probably don't show up in the long-term MRTG throughput graphs. I wonder what
queue lengths look like at millisecond resolution during these events.
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