Okay, it seems that it only happens when MIDI is set to 'raw' (not 'seq'), and the selected device is my Scarlett 2i4, so I'll just switch MIDI driver. I'll probably do more testing at some point.

Thanks for the guidance, I doubt I would've isolated the problem without it :)

On 12 December 2016 at 05:49, Thomas Howe <tho7maspenguin@gmail.com> wrote:

On 11 December 2016 at 15:03, Florian Paul Schmidt <mista.tapas@gmx.net> wrote:
You could try initializing it to something close to the max value :) Maybe even with attaching gdb to it if your executable has debug symbols (so you don't need to build it yourself).

Flo

I haven't figured out how to make jack with debug symbols, but I tried the perf record thing (attached) anyway. It looks from that like MIDI is a factor - in the previous tests I had the MIDI driver set to 'raw', but when set to 'none', there is no glitch after 6h 13m! I'm now repeating the test with 'seq'.

Instructions for initialising jack near the max value would be great! I'll look into gdb next time the spike occurs, which might be in 3h 30m...