Diffrent max latency results by LinuxCNC /HAL Latency Test or cyclictest

Hi guys:
I have installed armbian debian buster with PREEMPT_RT kernel 5.10.21-rt34-sunxi on orangepi pc board successfully. Thanks to MX_Master's work。
this
cyclictest result was fine after "abuse" it hardly.
it's 393us
which was fine. 
but when I switched to LinuxCNC  /HAL Latency Test (linuxcnc2.8.1)
It turn out 
851795ns(which is 852us) in Servo thread after "abuse" it. and some cases even worse. 
could any one tell me what happened ? which result I should belive in ?
Thanks a lot !
 

I don't think that is a matter of belief. Results are what they are.

Did you use isolcpus or something similar to isolate some core(s) for realtime tasks? Maybe worth a try.

The cyclictest results are pretty terrible. If you have isolcpus, something like
sudo cyclictest --mainaffinity=1 -a 2-5 -t -p80 -i10000

Where in my case 2-5 are the isolated cpus
I have found a reasonable correlation between latencytest and cyclictest

I remember some days ago reading this here. Maybe you could try the 5.10.110-rockchip-rk3588 kernel and isolcpu=5,7
forum.linuxcnc.org/18-computer/48079-can...cnc?start=220#273771