Reducing latency on multicore pc's - Success!

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07 Apr 2018 20:35 #108571 by Nemo1966
When adding the .conf to /etc/init is it supposed to start automatically when the pc starts? How can I verify it?

Thanks
Steve

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10 Apr 2019 08:21 #130592 by nicbit
Can somebody confirm the procedure described by Nebur could be used also for Debian 9.5 and LinuxCNC 2.7.14?

When I run manually /usr/local/sbin/set-irq-affinity 1-F (1-F is the hex mask where 1 is for CPU0) I obtaining sh: echo: I/O error.

Thanks,
Nic

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10 Apr 2019 12:36 #130596 by Todd Zuercher
I would say most likely not. This is a very old thread. The kernels used for his results were almost certainly an RTAI patched kernel, and I don't know of a RTAI patched version for Debian 9 (Stretch) unless you patched it yourself. The RT-Preempt kernels probably will not respond the same way.

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11 Apr 2019 07:17 - 11 Apr 2019 07:17 #130650 by nicbit
I follow this message forum.linuxcnc.org/38-general-linuxcnc-q...-preempt-not-working and I downloaded and installed linuxcnc-stretch-uspace-amd64-r13.iso (LinuxCNC 2.7.14) using a TB6660 board and 3 stepper motors as testing machine. The computer used is Dell Optiplex 360, Intel Core2Duo E7500 @ 2.93GHz, with 3 GB RAM, standalone NVidia video card, 250GB HDD. I tried to reduce as much as possible the latency. I followed the instructions provided by Nebur and seems is working except the set-irq-affinity script which is not starting automatically. Even so, my best result was 65250 ns. So, I would like to know if somebody else have better results. What can I do in order to minimize the latency? The LinuxCNC 2.7.14 based on Debian 9 Stretch is Ok?
Thanks,
Last edit: 11 Apr 2019 07:17 by nicbit.

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11 Apr 2019 14:26 #130663 by pl7i92
what latency do you got
the TB6600 can cope with 200.000 latency at a real good speed
this setup test here is at 24V only and can go at 160.000 Base tread
up to 1200deg/S²

im the Person how owns/runs the channel

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30 May 2019 22:50 - 30 May 2019 22:52 #135435 by vre
Asrock Q1900M Pro3
debian stretch / linuxcnc 2.8 pre1
root@mill:~# uname -a
Linux mill 4.19.0-0.bpo.4-rt-amd64 #1 SMP PREEMPT RT Debian 4.19.28-2~bpo9+1 (2019-03-27) x86_64 GNU/Linux

I had terrible jitter ( >200us) with with
GRUB_CMDLINE_LINUX_DEFAULT="quiet isolcpus=0,1"
but with
GRUB_CMDLINE_LINUX_DEFAULT="quiet isolcpus=2,3"
I have perfect jitter (< 17us)
Do not forget after that to run as root: update-grub
(you must edit /etc/default/grub)

The are huge differences in jitter on which cores you isolate.
isolating cores 0,1 does not work but isolating cores 2,3 gives perfect results.
Try it...

Has anyone an explanation why isolating cores 2,3 gives good jitter but not with 0,1 cores ?
Last edit: 30 May 2019 22:52 by vre.

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