[Cake] diffserv3 tin 2 target 50% of interval?

Pete Heist peteheist at gmail.com
Wed Feb 22 06:12:24 EST 2017

> On Feb 22, 2017, at 11:24 AM, Jonathan Morton <chromatix99 at gmail.com> wrote:
>> ... ‘interval' should generally remain at 100ms and that ‘target' should be computed at around 5-10% of interval, and preferably closer to 5%.
>> Is there a justification for setting the interval outside the guidelines suggested by CoDel’s authors?
> The interval is reduced on Tin 2 because it is intended for latency-sensitive traffic, which merits a more aggressive AQM response than for best-effort traffic, which tends to be more throughput-sensitive.  This has the happy side-effect of giving an additional incentive to not use latency-sensitive DSCPs for bulk traffic.
> It looks like you still aren’t using the latest version of tc, as that identifies the three tins as “Bulk”, “Best Effort”, and “Voice”, rather than numerically.

Ok, but for what it’s worth, so far I’m not seeing this confer any benefit as far as latency is concerned. I will make full results available later, but for now, here are two plots for the rrul test for diffserv3 and diffserv4, Cake on egress at 50Mbit between two Ethernet connected routers (no Wi-Fi):

http://www.drhleny.cz/bufferbloat/diffserv/rrul-rrul_cake_fd_50mbit-all_scaled.png (diffserv3)

http://www.drhleny.cz/bufferbloat/diffserv/rrul-rrul_cake_fd_50mbit_diffserv4-all_scaled.png (diffserv4)

Comparing the steady state portions of the plots for latency, they’re pretty much identical.

Also, shouldn't the EF flow (expedited forwarding) show lower latencies than BE (best effort)?

As for tc, I’m using the latest source from git://kau.toke.dk/cake/iproute2/, as per https://www.bufferbloat.net/projects/codel/wiki/Cake/. Shouldn't that be the latest or should I get it from somewhere else?


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