Bad latency performance ASRock Q1900B-ITX

Hi
actually wanted to build my Maho retrofit on a Q1900B-ITX board.
forum.linuxcnc.org/42-deutsch/42077-maho...plugandplay?start=30

now I am struggling with bad latency values.

the standard installation with Debian 10 Buster and PREEMPT-RT ISO Kernel delivers values between 100,000 and 200,000.
When I boot the installed RTAI kernel, the values are even worse.

I only got better values with a Debian 7 Wheezy RTAI Live Stick, 20000-25000


But now I don't really want to start with Debian 7


Is there anything else I could test or do I really have to get a new mainboard?

Are you using a usb-wifi adapter ?
That may be one reason for bad latency (driver problem). If so, try without it.

I tested one of those boards with different memory modules. If you can, test with different modules, it may affect the latency.
See here

There were some issues with the intel graphics driver too during the tests, can't remember the details. I think that disabling intel driver and using vesa resulted in better latency on preempt.

Disable all power savings and sound in bios. Note, at least the parport settings sometimes need a poweroff after changing settings in bios. This may be the case for other setting too, so it's safer to change the bios setting and power off. Then power on and test.
I'd also try to stop all unnessessary daemons and modules after installation. And use lightweight window manager (for example fvwm)

Thanks,
will test that in the evening.
Yes, I have a WiFi dongle plugged in, but I also tested with a cable, it may be that the times were slightly better, but still well over 100,000.
Keyboard and keypad also Logitech wireless USB dongle, which I actually wanted to keep on the machine afterwards.

I will test Vesa drivers.
Should I still isolate cores or was that only recommended for the RTAI kernel?

Or should I look around for more suitable hardware right away?
I bought the board especially for the retrofit, but before I put in endless time pointlessly and it doesn't go well anyway, should I replace it now?

I have to check the configuration later.
I have 3 of those boards, 2 with software stepping and one with a mesa 5i25.
One is still using the old 7, I just swapped the disk from the old P4...

that would be great thank you

I checked all 3, they are still debian 7. It must be so that I decided to go for the easy route while replacing the old P4s... just move the disk to a new pc.

I tried and installed from debian 10 buster preempt image to a spare ssd, latency test starts fine at ~5000 and climbs up to 150k-200k.
Changing the window manager from xfce to fvwm2 helped a bit but not significantly.

The test install was made with csm disabled in bios, it should not matter but booting in compatibility/non-uefi may help. Have to test that.

Many Thanks.
So it can be said that my board has no defect.

I will try to boot my kernel with isolcpus 0,1,2,3 in the evening.
could that help?

what else could i try?

Not all cores, max 1,2,3 to use only 0 for tasks.

Someone mentioned somewhere that the fans should be set to manual (I think it was full) without temperature control in bios. Also disable all sleep states etc power-savings related in bios.
I noticed that CSM disabled and sound disabled in bios Linux still loads sound drivers. So it may be nessessary to manually blacklist the driver that are not needed.

Easiest would be to use the old 7 because it's known to work.
I'll make more testing after work.

Quick test: I added "idle=poll isolcpus=2,3", reboot and test with 8x glxgears + youtube with a 2560x1440 monitor. About 1G/3.3G RAM used (this has only one 4G module, have to test with different memory configurations too).
Top shows core 0 & 1 ~5% idle, 2 100% idle, 3 ~35% idle.
Latency servo ~53k, base ~15k after about an hour.
Opening a new firefox window + another youtube did not affect latency values at all. Cpu usage increased a little.

Seems that isolating cores is the thing to do, probably need to go through different sets to check which one performs best.

Update: I tried different isolcpus and 1,2,3 gives best latency. 2,3 is the next best, now servo 31k, base 25k after 4 hours with same load as above. I'll let this run for tomorrow.