>Is this true of the LiveCD-distributed version of LinuxCNC, or only if

>using your linked code?

The RTAI tree for LinuxCNC (NTULINUX, me) has many fixes not included in RTAI 
mainline such as to the timer, math, scheduler, and HAL code. isolcpus is no 
longer required, I have thoroughly tested that branch myself across several 
64-bit SMP systems, 4 cores to 8 cores, and have had no issues, regardless if 
isolcpus is specified or not.


The tree hasn't been touched in awhile but it works as-is with LinuxCNC with no 
gotchas that I could find. isolcpus isn't necessarily "on" in that branch by 
default, it still works, but it isn't needed and can safely be left out.

I have not seen an instance where a real-time thread jumps across cores with 
that branch, with or without isolcpus, but I also have SCHED_MC and SCHED_SMT 
disabled. Enabling those and certain ACPI and IOMMU options may cause 
unexpected behavior, latency spikes, core jumping, etc.

This commit I assume fixes the issue of having interrupt remapping enabled 
(IOMMU option) with IPIPE enabled (instant boot failure after kernel 
decompression) but other problems may still remain depending on kernel 
configuration as the kernel patches (lazily) do not properly blacklist all the 
potentially conflicting options in Kconfig.


http://git.xenomai.org/ipipe.git/commit/?h=ipipe-4.1.y&id=1e5297761dd8d1c5b29d978863571ee62040a6af

Hope this helps!

Alec Ari

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