It's based on Linux 4.4.52 - the latest as of today; and from the same branch as the 710 kernel (4.4.35); and one of the LTS (long-term-support) version; patched with 4.4.50-rt63 patches.
I could manage only the "Basic RT" (PREEMPT_RTB) configuration. This is somewhat between "low-lateny" and "fully preemptible" configurations. I tried the "fully preemptible" (PREEMPT_FULL) configuration but while it gave me a kernel binary; it didn't work satisfactorily --- too many lockups at too unpredictable times.
It has been a very long time since I built an RT kernel (the last one was probably around Linux 3.4 days) which can run in fully preemptible manner. The RT patches aren't always stable either; depending on the kernel version they can be good, okay, or just bad; so I suppose for today, this is the best I can get.
Apart from changing the pre-emption level to PREEMPT_RTB, I made two more (unrelated) changes:
- I increased timer frequency to 1000 Hz.
- I added SDA_HWDEP support.
The first change is done because I plan to use the RT kernel for some audio work that requires lower latency and higher timer resolution.
The second one is done because by tweaking the codec's amplifier I could make my laptop speaker louder by using HDA Analyzer (which requires HDA_HWDEP support); but it turns out to be wishful thinking.
Anyway, enjoy. If you need a guide on how to use the new kernel, look here. There is a new way to test kernels without having to do all above, but it hasn't been written yet. I'll write it when I have time (and motivation) - basically you use "extrasfs" boot parameter to load the kernel-modules.sfs instead of replacing the kernel modules inside your initrd.
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