Mesa networking issues

Last weekend I was struggling with an underpowered PC to drive my Mesa 7i96 - so seeing PCW's recommendations in past posts, I have just acquired an HP Elite 8300 so I can make progress with my first LinuxCNC installation for a desktop mill. Unfortunately I have some networking problems, and would love some help.

I followed the recommended process and have a good installation of Debian Stretch with preempt-RT kernel, plus LinuxCNC 2.8. So far so good. I set up the BIOS as far as I could see to remove any power saving options. I turned off hyperthreading and the audio. (I haven't yet tried the grub file edits to change C-states and Isolcpus - but that will come later).

Next step were the edits to /etc/network/interfaces, as follows;

auto eth0
iface eth0 inet static
address 10.10.10.1
hardware−irq−coalesce−rx−usecs 0

After a reboot, the ping times were a slightly disappointing 0.3ms. So, I tried “sudo ethtool –C eth0 rx-usecs 0” at the command prompt, and pinged again. This time I was getting an average of 0.18ms per ping. So it looks to me like the entries in the /etc/network/interfaces file are not being enacted upon. I am a Linux newbie, so this was as far as I could go without asking for some help!

All the best
Graeme

The interfaces file looks right, note that the first ping (after some time) will be
longer because the host PC will first update its ARP cache with a ARP transaction

I get better than 180- usec on my test 8300, this may be CPU related
(I have the I5 3470s version) It may also be AMT related, so make sure
you disable AMT in the BIOS.

I should note that you can check for syntax errors in your interfaces file with:

sudo ifup --no-act eth0

Thanks for the fast response!

My machine is i3-2120 based, so I guess a little slower than yours is to be expected. And the first ping was slower as you suggest. I will certainly check the AMT setting too.

However my understanding was that the edits to /etc/network/interfaces and the ethtool command line operation achieve the same thing. But the command line operation halved the ping times, suggesting that the file edit wasn't doing its job. Is that a fair assessment? I understand that the file edit should offer a permanent setup for every reboot - the command line operation is just for testing - hence the file edit really needs to work!

Sorry, missed your last comment. Will go and take a look now.....

The ifup command came back with "interface eth0 already configured"....?

And AMT is disabled in the BIOS FWIW.

Just applied the CPU settings in Grub, and now have even more of a discrepancy! Right after reboot - with just the /etc/network/interfaces settings, I still get 0.3ms pings. But after the ethtool command, the max ping time (from 50 tries) was 0.102ms. The majority were sub 0.1ms. So this machine can ping fast - but only when provoked!

Any suggestions for a permanent fix most welcome!

Graeme

Not sure why your interfaces file setting does not work
They do work for me, here is my interfaces file:

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

auto eno1
iface eno1 inet static
address 10.10.10.100
hardware-irq-coalesce-rx-usecs 0

(I have a different Ethernet device name)

You can check your current coalescing settings with
ethtool -c eth0

Also you might try running ifdown and ifup manually to see if ifup changes the coalescing settings
(and also delete any network manager devices that might interfere)

Thanks for the thoughts. I'll go and have a play.

Just one thing to mention - I have a USB WiFi dongle plugged in and configured using the Network Manager. I have been struggling to get that to connect and be reliable - sometimes it's perfect, other times just fails to connect. A problem for another day - but maybe worth mentioning in case it has a bearing here.

The ethernet interface part of Network Manager just says it is unmanaged, and I haven't touched that. I assumed it was ok for the wifi to be controlled via the Network Manager, and the ethernet by the /etc/network/interfaces file - but is that the case?

Can I (should I) set up the WiFi from /etc/network/interfaces too?

I think I would leave the WIFI managed by the network mangler
reporting "unmanaged" is a good thing, that means its leaving
the interfaces file controlled devices alone.

ifquery might be useful also