Weird network performance problem

[Chavdar Ivanov <ci4ic4%gmail.com@localhost>]

Hi,

My home network is rather simple - on each floor there is a gigabit
switch; these are linked with a gigabit powerline adapter, the actual
speed between the two nodes is always around 150mb/s. The router/WiFi
a/p is connected to the downstairs switch; my everyday laptop (T) uses
WiFi, W10 claims the speed to be 866.7Mbps.

On the upstairs network there is a NetBSD-current amd64 laptop (Y)
connected only via the wired connection at 1000Mbps:

wm0: flags=0x8b43<UP,BROADCAST,RUNNING,PROMISC,ALLMULTI,SIMPLEX,MULTICAST>
mtu 1500
        capabilities=0x7ff80<TSO4,IP4CSUM_Rx,IP4CSUM_Tx,TCP4CSUM_Rx>
        capabilities=0x7ff80<TCP4CSUM_Tx,UDP4CSUM_Rx,UDP4CSUM_Tx,TCP6CSUM_Rx>
        capabilities=0x7ff80<TCP6CSUM_Tx,UDP6CSUM_Rx,UDP6CSUM_Tx,TSO6>
        enabled=0
        ec_capabilities=0x17<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,EEE>
        ec_enabled=0x3<VLAN_MTU,VLAN_HWTAGGING>
...

There are also an XCP-NG server (X):

$ uname -a
Linux xcp-ng-ci 4.19.0+1 #1 SMP Fri Jul 19 17:27:05 CEST 2019 x86_64
x86_64 x86_64 GNU/Linux
$ cat /etc/centos-release
XCP-ng release 8.0.0 (xenenterprise)

Another laptop, at present running the latest Fedora, again gigabit
wired (B), and, for good measure, another 6-7 domU's running under the
XCP-NG host.

I test the network speed using iperf3 on all these boxes. The speeds
upstairs, where all the machines are connected to the gigabit switch,
are roughly consistent - I get some 930Mbps both ways (there is a bit
of a speed ramp-up when the server is the NetBSD laptop, but after the
fifth or so transfer it gets to the same rates). The speeds are also
consistent if I setup the W10 laptop as iperf3 server - through the
powerline adapters and them the WiFi - I get between 130-150 Mbps from
all of them.

The weird problem for me is when using the W10 laptop as a client and
all the hosts upstairs as servers; all the speeds are consistent
around the same 130-150Mbps range, with the exception of the
NetBSD-current laptop - which consitently give me about 20-30Mbps,
some 4-6 times slower than the rest. I suspect this has happened
recently - as I noticed it using the NetBSD laptop as NVMM host and
seeing the guests appear on the VNC server downstairs as very slow -
and even saw losing my VNC links completely, which wasn't the case
before - I used to run some 4-5 NVMM guests on this laptop at the same
time.

To complement the above - The Fedora laptop (B) also runs W10. Iperf3
returns the expected figures - about 930Mbps as on the same gigabit
switch - when it connects to the XCP-NG host (X) and the FreeBSD
guest; when tested against the NetBSD laptop (Y) on the same switch,
it returns only a third of the above - around 320Mbps. On the other
hand, if (B) is under W10 and iperf3 is server, the connection from
the NetBSD laptop is full speed.

So it seems for some reason the NetBSD laptop does not perform well
with the W10 client, no matter what the type of connection. All other
interconnections appear as expected - Linux to all the others, W10 to
Linux, FreeBSD and other W10, etc. It is only W10 to NetBSD appearing
3-5 times slower than the rest. This was confirmed with a
NetBSD-current guest of the XCP-NG host - to which I again get the
same figures as to the bare-metal NetBSD laptop - it returns about
30Mbps, whereas a FreeBSD guest on the same host returns about
130Mbps. The XCP-NG NetBSD guest is HVM, though, and even if the
interface is wm and recognized as 1GB, it doesn't return more than
about 70Mbps, even to the other XCP-NG guests (still better than from
the W10 laptop).  The FreeNAS guest is

Any reasons for this and perhaps some pointers to sort this out?

Apologies for the rather long message.

Chavdar

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