Mesa networking issues

So initial feedback is that "ethtool -c eth0" reports a value of 3 for rx-usecs after bootup - and then a value of 0 when I run the command line setting. So my /etc/network/interfaces is definitely not working. Its contents are exactly like yours apart from the ethernet interface name, and the fact that my static IP address is set to 10.10.10.1.

And then there's my WiFi dongle set up in the Network Manager. If that's an issue....

That's very strange

Could you you reboot, check the rx-usecs then run sudo ifdown and sudo ifup
and see if that changes the setting

My setup has a USB WIFI dongle managed by the network manager
and that does not cause an issue with my interfaces file functionality

What OS are you running?

Just done what you requested. The ifup took a while, as it was waiting for DHCP - I presume that is what is expected? Otherwise, the rx-usecs was 3 before and after. Unchanged.

Sorry, I'm running Stretch with preempt-RT kernel, LinuxCNC 2.8.

There is no reason to DHCP to be involved, and running
sudo ifup [device]
takes only a fraction of a second on my machine

for example

sudo ifdown eno1
sudo ethtool -C eno1 rx-usecs 50
ethtool -c
....
rx-usecs: 50
....
sudo ifup en01
ethtool -c
....
rx-usecs: 0

What OS are you running?
Did you show the entire contents of the interfaces file?
Worst case you could add the ethtool command to the startup script
but that really should not be needed

EDIT I wonder if this is a clue:
In my email I got this response from your forum post:

auto eth0
iface eth0 inet static
address 10.10.10.1
hardwareirqcoalescerxusecs 0

Notice the missing "-"s

Is it possible you have somehow corrupted the command with non ASCII characters?

I ran your sequence of operations, and it all matched apart from the last part;

sudo ifup eth0
Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit www.isc.org/software/dhcp/

Listening on LPF/eth0/d8:d3:85:93:3b:21
Sending on LPF/eth0/d8:d3:85:93:3b:21
Sending on Socket/fallback
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 7
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 8
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 12
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 13
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 10
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 11
No DHCPOFFERS received.
No working leases in persistent database - sleeping.

The above took maybe 30 seconds, at which point it appears to have given up and come back to the prompt.

sudo ethtool -c eth0
rx-usecs: 50

The interface works though, and I can ping 10.10.10.10 no problem.

I'm running Stretch with preempt-RT kernel, LinuxCNC 2.8.

My interface file in its entirety is as follows;

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# Ethernet port setup for Mesa card
auto eth0
iface eth0 inet static
address 10.10.10.1
hardware−irq−coalesce−rx−usecs 0

Just to be sure!

uname -a
Linux novamill 4.9.0-8-rt-amd64 #1 SMP PREEMPT RT Debian 4.9.110-3+deb9u6 (2018-10-08) x86_64 GNU/Linux

OK your last post shows something is wrong with your

hardware−irq−coalesce−rx−usecs 0

text. How did you edit the file?

I'll check your non-ASCII theory - can't remember if I pasted that in from the manual or typed it. Stand by.....

Sir, you are a true Genius! That is what it was. I overwrote the dashes with new ones - the old ones were longer than the new ones, and rebooting made it behave as expected with rx-usecs set as 0. I have super fast pings now - typically 0.1ms - which was what I'd hoped for.

I think I pasted the text from the manual, but I really can't be sure. My bad whatever. But bad characters is what it was. So, now on to the HAL set up....

Many, many thanks for your help on that. Much appreciated!

Cheers
Graeme