Debian – How to run real-time application in Linux

debianreal time

Trying to get working LinuxCNC on my Debian Jessie, I did:

Installed the kernel 4.9 RT through Jessie backport using apt-get/aptitude.
Restarted my computer and checked uname -a contain PREEMPT RT
Installed LinuxCNC by adding the repository and using apt-get

After that, starting the linuxCNC wizard (by normal clicks through menus) there is a jitter test. My current results are absolutely bad, around 140us.

I wonder if there is any PREEMPTION configuration to enable, or specific way to run an application to get more precise real-time?

Also, how could I check that the process is running real-time?

Note: My computer is an intel E6600

Best Answer

I wonder if there is any PREEMPTION configuration to enable, or specific way to run an application to get more precise real-time?

See the following:

http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Latency-Test

which links to this:

https://forum.linuxcnc.org/18-computer/25927-reducing-latency-on-multicore-pc-s-success?limitstart=0

(from the above page:)

Linux related changes:

edit /etc/default/grub and add the kernel options: "isolcpus=1 acpi_irq_nobalance noirqbalance" (call update-grub afterwards)

make sure that the software "irqbalance" is NOT installed, remove if it is there (Ubuntu software center -> installed software -> search for irqbalance -> remove)

add the upstart script "irq-affinity.conf" to /etc/init (see attachments, it will move the irq-handling to the first core)

add the sh scripts set-irq-affinity and watchirqs to /usr/local/sbin (first allows to set the affinity mask manually, second opens a console window that shows live how the irqs are scheduled to the different cores -> all numeric irqs but 0 should be handled by cpu0)

You might have to adapt the script for Système D, though ...

A quick thing to test: You could also up the priority with nice -n <x>, where <x> is the desired priority.

Also, how could I check that the process is running real-time?

See this question: Real time processes scheduling in Linux

Related Solutions

Linux – real time backup if file changed

You could probably hack this together using inotify and more specifically incron to get notifications of file system events and trigger a backup.

Meanwhile, in order to find a more specific solution you might try to better define your problem.

If your problem is backup, it might be good to use a tool that is made to create snapshots of file systems, either through rsnap or a snapshoting file system like xfs or using any file system with lvm.
If your problem is sycronizing, perhaps you should look into distributed and/or netowrk file systems.

Edit: In light of your update, I think you are making this way to complicated. Just make a folder in your dropbox for scripts. Then in your bashrc files do something like this:

export PATH=$PATH:~/Dropbox/bin
source ~/Dropbox/bashrc

Whatever scripts you have can be run right from the dropbox folder in your home directory, and any aliases and such you want synced can go in a file inside Dropbox that gets sourced by your shell.

If other people besides you need access to the scripts, you could symlink them from your Dropbox to somewhere like /usr/local/bin.

Real Time Local File Sync

A filesystem overlay would probably work better for this. Using something like aufs you can create a 'virtual' directory out of several combined directories. You can configure whether writes should propagate back to the original directories, or use a copy-on-write method to leave the originals alone, or disallow writes altogether.

However to answer your original question, you can use something like lsyncd to trigger an rsync as soon as a file is modified. lsyncd uses rsync, which is capable of syncing directory contents without keeping the directory name. Generally the way to do this is to sync sourcea/. to /some/destdir/. The important part is the dot at the end of the source path. This is a general trick that can be used for things other than rsync, like cp.

Best Answer

Related Solutions

Linux – real time backup if file changed

Real Time Local File Sync

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