Dave Täht writes:
> What kernel is this, btw? A *lot* of useful stuff just landed in
net-next for network namespaces, which may mean I can try to validate
your results in emulation, also. My primitive (eyeballing the packet
captures of some tcp traces) jitter result in a 4 virtualized network
namespace, was 2-6us, but that's hardly trustable.
4.9.0-4 (Debian Stretch). I only now read the man page for ip-netns for the
first time. After re-reading your post about using this to consolidate the test
environment, I get it now. That could be extremely helpful, though at first
glance I wonder about the realism of netem (depending on how it's being used).
> Knowing that basic measurement noise in your setup is < 107us is quite
helpful, I wonder what the sources are....
Good question and I'd also like to know. I could have included full stats to
show that server processing time is part of it. Here's another run:
```
sysadmin@apu2a:~$ ./irtt client -i 1ms -d 10s -q 10.9.0.2
[Connecting] connecting to 10.9.0.2
[Connected] connected to 10.9.0.2:2112
Min Mean Median Max Stddev
--- ---- ------ --- ------
RTT 233µs 269µs 268µs 330µs 8.69µs
send delay 119µs 135µs 134µs 190µs 6.74µs
receive delay 103µs 134µs 134µs 176µs 5.12µs
IPDV (jitter) 0s 8.47µs 6.08µs 92.3µs 7.98µs
send IPDV 0s 6.25µs 4.29µs 56.9µs 6.62µs
receive IPDV 0s 4.62µs 2.99µs 64.1µs 5.15µs
send call time 16.1µs 28.7µs 57.1µs 3.01µs
timer error 0s 4.55µs 121µs 5.09µs
server proc. time 14.8µs 16.3µs 68.8µs 2.97µs
duration: 10s (wait 989µs)
packets sent/received: 10000/10000 (0.00% loss)
server packets received: 10000/10000 (0.00%/0.00% upstream/downstream loss)
bytes sent/received: 600000/600000
send/receive rate: 480.0 Kbps / 480.0 Kbps
packet length: 60 bytes
timer stats: 0/10000 (0.00%) missed, 0.45% error
```
Server proc. time is the time between after after the server receives the
packet and right before it sends it (dual time stamps are enabled here).
Theoretically I could somehow set the Linux thread scheduler to SCHED_FIFO and
increase the sched_priority value, but:
- I'd probably have to lock the goroutines to OS threads, which I can do
(already have a -thread option for both client and server)
- It's not clear to me how to set SCHED_FIFO and prio without a bit of native
code compiled in
- I'm not sure it would even help
It'd be interesting to see if you run the same irtt command in your namespaced
environment, what you'd get.
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