latency test question

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09 Jul 2021 01:33 #214058 by kelargo
hello,

I am reading this web page on using the latency test utility.
linuxcnc.org/docs/html/install/latency-test.html

and I am wondering if there is a typo in the page?

The picture displayed shows two rows. "servo thread" and "base thread".
In the text below, it makes reference to " 9075 nanoseconds, or 9.075 microseconds."

and with rounding the numbers in the .png file, no numbers are close to that number?
The Max Jitter for the "servo thread" is 4578 and the max jitter for the "base thread" is 6693.

I am a bit confused over this. I suspect the .png was updated but the text was not ?
The text also just says the max jitter is important.  is it the max jitter for the base thread or servo thread? 
or the sum of the two threads ? 

thanks


 

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09 Jul 2021 07:41 #214065 by tommylight
Replied by tommylight on topic latency test question
Base thread or period is mostly used for parallel port machine control so for Mesa boards and some other controllers it is not required, those use just the servo period, so if you plan on using them type this in a termal:
latency-histogram --nobase --sbinsize 1000 --show

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09 Jul 2021 11:59 - 09 Jul 2021 13:05 #214083 by kelargo
Replied by kelargo on topic latency test question
Thank you.  with that command, I get this displayed.  I plan on using MESA 7I76E.

But I guess the documentation has a typo, with the picture showing 4578 Max Jitter for servo thread and the text referencing 9075 ns as the Max Jitter? 

On my machine, I cranked up glxgears to over 100 instances and the deviation pretty much remained unchanged.
Im accessing my machine with x2go, if that contributes anything and removed wifi, which significantly lowered jitter.

I would use a Max Jitter of 40 micro sec (us)?

 

before removing wifi

 


 
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Last edit: 09 Jul 2021 13:05 by kelargo.

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09 Jul 2021 13:24 #214097 by andypugh
Replied by andypugh on topic latency test question
Thanks for the report. The docs have been updated and the change should be visible in a few hours.
The following user(s) said Thank You: BigJohnT, kelargo

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09 Jul 2021 14:58 #214116 by tommylight
Replied by tommylight on topic latency test question
That is all very good, so forget latency and start wiring stuff, we want chips ... i'm hungry ! :)
The following user(s) said Thank You: kelargo

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