lcnc2.9 latency-test bug ?

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02 Jan 2020 17:22 #153799 by tuxcnc


It is after launch the latency-test, and of course the values are not possible.

I suspect a bug, that causes "rtapi error" messages after run axis or other gui.
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02 Jan 2020 18:15 - 02 Jan 2020 18:21 #153801 by Todd Zuercher
Are you sure you are running a realtime enabled kernal?
What result does the command "uname -a" show in a terminal?
Last edit: 02 Jan 2020 18:21 by Todd Zuercher.

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02 Jan 2020 19:21 - 02 Jan 2020 19:27 #153804 by tuxcnc
Replied by tuxcnc on topic lcnc2.9 latency-test bug ?

Are you sure you are running a realtime enabled kernal?

This is 4.14.148-rtai-amd64 patched from github.com/NTULINUX/RTAI/ and compiled myself.
It is of course realtime and gives extremely low latency, not exceed 5000 on my hardware.
Picture I attached shows not impossible situation, because max_interval=base+max_jitter.
If jitter is 25000 and base is 25000 than max interval should be 50000.
So, at start, jitter measure must be bad, I suppose.
Maybe it is the same reason to "rtapi error" message at start of linuxcnc gui ?


This is a good measure, after "Reset Statistics" :
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Last edit: 02 Jan 2020 19:27 by tuxcnc. Reason: add picture

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02 Jan 2020 20:00 #153809 by Todd Zuercher
I'm not so sure the Max Interval needs to necessarily be equal to sum of the Max Jitter and thread time, because the time intervals before and after the Max Jitter point may have been significantly shorter than planned.

Regardless, perhaps running the Latency-histogram or Latency-plot might be more telling (specifically the Latency-plot.)

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13 Jan 2020 17:26 #154773 by tuxcnc
Replied by tuxcnc on topic lcnc2.9 latency-test bug ?
Another curiosum - interval=210ns
This is Ryzen5 3400G/Gigabyte A320M-S2H V2, kernel 5.2.21-rt13, Xubuntu 18.04

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