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Preemptive RT on Jessie or Stretch?

  • tommylight
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07 Jul 2018 08:38 #113667 by tommylight
Replied by tommylight on topic Preemptive RT on Jessie or Stretch?
Consider this a message !
I do not like writing to e-mails, they are private and should remain so. I have had plenty of forum users sending me e-mails with the same questions as here on the forum. And therein lies the problem as if i reply to them they get my e-mail address so the spam runs rampant ! Already had one private email made useless after several years of use by some users on some other forums.
Usually i give my mobile phone number way easier than the e-mail.
Unfortunately this forum does not have private messages.
Make it available for a limited time on google drive or similar and remove it after the time expires.
Thank you.
Tom

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07 Jul 2018 09:33 #113670 by AnnoyingMutt
Replied by AnnoyingMutt on topic Preemptive RT on Jessie or Stretch?
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07 Jul 2018 17:41 - 07 Jul 2018 17:42 #113732 by andypugh
Replied by andypugh on topic Preemptive RT on Jessie or Stretch?

So, since last asking in May, has anybody else gotten Jessie/Stretch working?


Yes, by the simple expedient of using the LinuxCNC Stretch live-DVD.

www.linuxcnc.org/testing-stretch-rtpreempt/
Last edit: 07 Jul 2018 17:42 by andypugh.

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28 Aug 2018 10:18 #116713 by twoflowers
Replied by twoflowers on topic Preemptive RT on Jessie or Stretch?
I tried the linked isos. While they work, it's not an enlightment. The latency figures of the 4.9 RTPREMPT kernel are plain horrible compared to the RTAI kernel (about 5 to 10 times higher).

I alsotried upgrading from wheeze->jessie->ascii/stretch. This works, but the RTPREEMT kernel ... Anyhow, now I run devuan ascii on the wheezy kernel. While axis from wheezy works on jessie, it fails on ascii/stretch. gmoccapy works, but I need axis :/

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28 Aug 2018 10:36 #116714 by PCW
Replied by PCW on topic Preemptive RT on Jessie or Stretch?
What hardware do you have? recent Preempt-RT kernels can have very good latency figures on the right hardware:

freeby.mesanet.com/8300-4.18.png

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28 Aug 2018 10:50 #116717 by twoflowers
Replied by twoflowers on topic Preemptive RT on Jessie or Stretch?
I ran this on T60/T61 C2D, one with ATI and the other with Intel GPU. Latency on RTAI is ~ 5.000ns, on RTPREEMT ~ 70.000ns. I get the same figures on my old Desktop (gigabyte+xenon). What is more troubling on the Intel boards: I cannot turn off SMI any more. This gives additional 450.000ns peaks every now and then. I would not see this as a problem if that very same hardware would not have worked before.

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28 Aug 2018 11:23 - 28 Aug 2018 11:27 #116721 by PCW
Replied by PCW on topic Preemptive RT on Jessie or Stretch?
Heres a recent Preempt-RT running on a C2D desktop
(10 glxgears +running youtube videos)



Not sure what the SMI issue is...
SMI seems to not be used at all on modern desktops (I've never needed to use a SMI workaround on intel CPUs)
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Last edit: 28 Aug 2018 11:27 by PCW.

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28 Aug 2018 17:28 - 28 Aug 2018 17:29 #116745 by twoflowers
Replied by twoflowers on topic Preemptive RT on Jessie or Stretch?
Ok, these are my figures: Testsubject is my T61 with intel gpu. I booted the official 2.7 linuxcnc dvd, this is the latency out of the box:



This is the same computer, this time I booted the strech dvd from your link (amd64) - no glxgears this time, running those does not change the numbers:

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Last edit: 28 Aug 2018 17:29 by twoflowers.

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28 Aug 2018 18:42 - 28 Aug 2018 18:44 #116750 by PCW
Replied by PCW on topic Preemptive RT on Jessie or Stretch?
Well its not so good on RTAI either (512 usec)

That does look pretty terrible though possibly your CPU cannot run a 40 KHz thread with Preempt-RT so everything is broken

(trying with servo thread only would show if this were the case)
Last edit: 28 Aug 2018 18:44 by PCW. Reason: Minimum time doesnt mean that due to the way its calculated

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29 Aug 2018 01:52 - 29 Aug 2018 02:04 #116763 by twoflowers
Replied by twoflowers on topic Preemptive RT on Jessie or Stretch?
Oh, these spikes are from SMI and go away when I disable SMI with smictrl. As it's not included in the DVD, I didn't bother.

This is from a X200

So, what hardware is needed for Rreempt-RT? Are all CPUs alder than 10 years out of the game?
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Last edit: 29 Aug 2018 02:04 by twoflowers.

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