Pentium J2900 fanless pc test results

Hi Guys,

greetings from New Zealand. First post please don't judge too harsh.

Wanted to share some results of my experiments with a cheap fanless pc i got from AliExpress for 89usd including shipping.

Don't know the seller just chose the cheapest. 

Specs: Pentium J2900 4 cores, 2 Lan ports, 4Gb Ram, 128GB SSD, Wifi. 
Mesa board: 7i96s

Used standart 2.9.4 Debian 12 Preempt-rt ISO with 6.1.0-30-rt-amd64 #1 SMP PREEMPT_RT kernel.

List of changes i made:

1. Physically removed internal Wifi board. (plan to use usb dongle)

2. Disabled everything in BIOS.

3. Network is Realtek so had to replace the driver. 

Included r8169 driver is a big no no, so here is what i did:

•     deleted all r8169 related ko files from /lib/modules/6.1.0-30-rt-amd64/kernel/drivers/net/ethernet/realtek (there were 3)
•     Since this machine is not connected to the network i compiled r8168.ko using dkms in a VM with the same kernel and copied this one file to the above folder.
•     ran sudo depmod to refresh the tree.

4. Kernel adjustments are all in /etc/default/grub
    
    GRUB_CMDLINE_LINUX="irqaffinity=0-1 kthread_cpus=0-1 isolcpus=domain,managed_irq,2-3 rcu_nocb_pol pcie_aspm=off r8168.aspm=0 r8168.eee_enable=0 modprobe.blacklist=r8169,mei_txe"

5. changed /etc/lightdm/lightdm.conf for autologin - autologin-user=dm


the results with latency, pings and temperature are attached.


PS. I did see some occasional single pings over 1ms, very rare, may be one in an hour or even less. interestingly there are no requests in 0.5-1 range, it stays well under 0.5ms and then has 1.2-1.5 ms or so just for a single request. Could be just noise. I suspect the no name SSD does not help, but at this point don't see the need for upgrade.  Will update if this will get worse or cause any troubles in real use. 

Cheers,
DM

Removing the Wifi board is probably good for latency.
The DKMS driver can usually be installed with 

sudo apt install r8168-dkms
but you do need to have non-free in the apt sources. This is included in the Linuxcnc ISO

the internal wifi card sits on the same pci bus as hard-drive and ethernet, so its driver can easily throw a wrench into the latency. I could probably just blacklist its driver in grub from loading, but i chose to completely remove it.

yes, sudo apt install r8168-dkms will work fine if you have your controller connected to the internet. I did not, so i used that command to build realtek 8168 driver on a virtual machine connected to the internet. (which in fact is just one file called r8168.ko) then i copied this file over to the controller using usb stick and manually replaced the default driver.

I don't plan to upgrade the kernel any time soon, so this approach works for me.