I did some more testing. Same setup as before, I varied the amount of delay:

server        --        delay        --        mbox        --        client
netserver             Xms/Xms             45/900mbit

Cake config:
qdisc cake 801b: dev mbox.l root refcnt 2 bandwidth 45Mbit diffserv3 triple-isolate ack-filter-aggressive rtt 100.0ms noatm overhead 38 via-ethernet mpu 84
qdisc cake 801c: dev mbox.r root refcnt 2 bandwidth 900Mbit diffserv3 triple-isolate rtt 100.0ms noatm overhead 38 via-ethernet mpu 84

Results:
delay 10ms (rtt) flent: https://drive.google.com/open?id=1hq_MRtocoDglTqxvAHoZvo932ThLBQaC
delay 10ms (rtt) stat: https://drive.google.com/open?id=1kTnpreQzpRn-7iO6i85eXVf8GjJYg19e

delay 20ms (rtt) flent: https://drive.google.com/open?id=1Ollbqg7BzM4RiPuSH-tiIuaE8vnKu5tg
delay 20ms (rtt) stats: https://drive.google.com/open?id=1nwS80SJmnVtubIXyYgBCIQdom_QfSSKB

delay 40ms (rtt) flent: https://drive.google.com/open?id=1nWUo82_L8_GobR1xbKms-jGhkNwT5msx
delay 40ms (rtt) stats: https://drive.google.com/open?id=1oYfERh57fKHomVHb4z0dHQtFtP2U2aWs

delay 80ms (rtt) flent: https://drive.google.com/open?id=17j2T12Xmbi10i-0drHOgdc1x1NL8zAto
delay 80ms (rtt) stats: https://drive.google.com/open?id=1e8cf5z4xDXYMbY8Q1rMvJd8J8F5OOcth

delay 100ms (rtt) flent: https://drive.google.com/open?id=1vg-A92eFc7AMSOuBgj-sRnANBMJda9og
delay 100ms (rtt) stats: https://drive.google.com/open?id=1_WojJPa8h9JmNvmWjW9Gos8ShtvM-zt0

I will repeat these with ack-filter instead of ack-filter-aggressive.

George


On Wed, Nov 29, 2017 at 10:44 AM, Toke Høiland-Jørgensen <toke@toke.dk> wrote:
> (That was also informative for me about how netperf decides when to
> emit a data point…)

In that case I can add that the stated reason for this way of doing
things is performance (i.e., emitting data points should not interfere
with transfer performance). This is mostly an issue on systems where
getting time is expensive; which is not the case on modern Linux
systems. But I'm not entirely sure that the optimisation only has
historical reasons; it may be that some systems supported by Netperf
still has this issue...

-Toke