Comment 59 for bug 1670041

Using ubuntu 17.10, kernel 4.13-0.15-generic on XPS 13 9360 QCA6174 rev 32.
Connection on 5Ghz band AC Freebox router.

Had the same problem, however browser speedtest [1] worked fine, except that any upload on nfs or cifs were from 0 to max 1MB/s with system freeze when uploading big files.
Changed in networkmanager the MTU to 1400 (trial and error) and now the upload speed on nfs is around 25 MB/s.

Iperf still gives bad results for uploads. On NFS the speed increases from 2 MB/s - 25MB/s in about 5 seconds, so it seems that the TCP algorithm is/was the problem here.

[1] http://www.speedtest.net/my-result/6703944909
http://pic.nperf.com/r/184530901-oTbTp0X2.png

The WIFI is the bottleneck here as over Ethernet I get ~ 500mbps/200mbps.

I hope this helps.