https://bugs.freedesktop.org/show_bug.cgi?id=91308
--- Comment #4 from Christian König deathsimple@vodafone.de --- (In reply to Andy Furniss from comment #3)
It seems that I can make it work reliably by setting my cpus to perf with cpufreq.
Sounds like some kind of race condition to me, e.g. something isn't properly protected and multi thread save.
That's probably pretty hard to find.