On 21/09/16 13:40, Mikael Abrahamsson wrote:
On Wed, 21 Sep 2016, Dave Taht wrote:
* It seriously outcompetes cubic, particularly on the single queue
aqms. fq_codel is fine. I need to take apart the captures to see how
well it is behaving in this case. My general hope was that with fq in
place, anything that was delay based worked better as it was only
competing against itself.
I'm looking at 4up-sqwave-fq_bfifo-256k. Is this really fq_bfifo, or
just bfifo? Looks like there is no fq.
the queue before the (simulated) _bottleneck_ is simple bfifo.
sch_fq is used on the _endpoint_, because it's a requirement of tcp-bbr
It's disambiguated by knowing you don't add child qdiscs to sch_fq, and
no-one has written a linux qdisc called fq_bfifo.
If someone doesn't have the correct Flent available, I posted two
screenshots here: http://imgur.com/a/cFtMd
What I think I see:
The flows are started in order: "BBR1, CUBIC2, BBR4, CUBIC3" (a bit
confusing, but according to your description).
So it looks like BBR1 fills the pipe within half a second or so, nice
steady state. Then CUBIC2 starts, and slowly over a few seconds,
starts to starve BBR1 of BW, it looks like steady state here would be
that CUBIC2 would end up with around 65-70% of the BW, and BBR1
getting 30-35%. Then BBR4 comes along (10 seconds in), and just KILLS
them both, smacks them over the head with a hammer, taking 90% of the
BW, wildly oscillating in BW way above 20 megabit/s down to 10. The
ping here goes up to around 150-160ms. CUBIC3 starts at 15 seconds and
get basically no bw at all.
Then at around 22 seconds in, I guess pretty close to 12-13 seconds
after BBR4 was started, BBR4 starts to calm down, slowly letting the
other streams come back to life. At around 30 seconds, they all seem
to get at least a bit of the bw each and nobody is completely starved,
but BBR1 seems to not get much BW at all (very dotted line).
When at the end there is only CUBIC3 and BBR4 left, it looks like BBR4
has a 2/3 to 1/3 advantage.
Looking at cake_flowblind_noecn, BBR1 and BBR4 just kills both CUBIC
flows. Same with PIE.
So it seems my intuition was wrong, at least for these scenarios. It
wasn't CUBIC that would kill BBR, it's the other way around. Great to
have testing tools! Thanks Flent!
wow. I was wondering how BBR ever relinquished bandwidth. "With some
difficulty".
Though not in the second screenshot where there's a strict AQM (cake
flowblind). Then it shares with other BBRs while never letting CUBIC
get established. (I think if you look at drops, they'd be higher than
what 4xCUBIC converges to on that link. See
https://groups.google.com/forum/#!msg/bbr-dev/EXgiWxHvaEU/wl3Q39svAAAJ ).
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