latency spike up need help

Recently, i get a new PC with this config:



After installing ubuntu 16.04, realtime preempt-rt 4.9.84 kernel, and linuxcnc, i try test latency then it gives me a very disappoint number:


The latency spike up random, I tried many solutions:
1: Disable SMI control -> doesnt work
2: Disable ACPI and usb legacy support in BIOS
3: Disable core and hyper threading, my PC can run a few minutes with low latency then spike up random.
After it spike up, i try click "Reset statistcs" on latency-test but it still keep that high value

This is the first time i cant fix latency by above solutions. Are there any solutions that i can try? please give me some. thank you

Did you disable all CPU speed switching/power management
in the BIOS (Limit C states to C1 max etc)?

Try this:

wiki.linuxcnc.org/uploads/07_rtai

you can try to get smictl to help you find a good solution

Thanks all for help guys,

Today i found out in BIOS there is a "SMI lock" in chipset section. After enabled it latency seem work ok.The smictl maybe doesnt work in this PC. I will try more test to confirm it.

After reseting PC, latency spike up again

thang wrote:

Thanks all for help guys,

Today i found out in BIOS there is a "SMI lock" in chipset section. After enabled it latency seem work ok.The smictl maybe doesnt work in this PC. I will try more test to confirm it.

After reseting PC, latency spike up again

Exactly the latency is still ok when i run latency-test, but when i run linuxcnc that has classicladder ( using modbus as slave) i got "Unexpected realtime delay" even my servo thread is 500us, classicladder's thread is 10ms and didnt connect to master yet.

It happened not right away and only in this PC, do you think what can cause this problem?