runaway latency detection

T. Smith tlsmith3777 at
Sun Aug 21 19:22:37 PDT 2016

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?

More information about the irqbalance mailing list