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Ingo Molnar wrote:

John Sigler wrote:

quoted

quoted

With a pair of the following in the middle:

softirq--4     0....  670us : call_rcu (rt_run_flush)
softirq--4     0D..1  670us : __rcu_advance_callbacks (call_rcu)

quoted

Any idea what went wrong in the above function trace? Why is the 
kernel spinning in circles that way?

does your test-app have higher priority than softirq--4 ?

PID 4 is [softirq-timer/0] and has priority 50 in SCHED_FIFO.
My process has priority 80 in SCHED_RR. It is waiting for IRQ10.

My user-space app has higher priority than everything except
PID 2 which is [posix_cpu_timer]

Is this a priority inversion issue?

Regards.