runaway latency detection

[T. Smith]

Trying to isolate PREEMPT_RT (full preemption) runaway latency conditions seen when using the cyclictest on the 4.1.8 SMP PREEMPT_RT kernel.  Seen average latency of 3uS, but runaway or outlier max latency random spikes seem indeterminate.  Noted 72uS with one run of the cyclictest for example. Is this a known issue, the cause understood, and is there a patch for this?   This is on ARM8 Cortex-A53 four core. Running the cyclictest on an isolated core 2 or 3 shows same behavior as do other platforms.  No Trusted OS configured.

The goal is to isolate causes of indeterminism when using the PREEMPT_RT kernel configuration with full preemption and to characterize latency and jitter using ftrace, any recommendations on catching random latency spikes using ftrace or profiling when running the cyclictest?