Kernel schedules kernel tasks on isolated cpus, SCHED_FIFO prevents kernel tasks from running

[Rik van Riel]

On Wed, 2017-06-28 at 08:39 -0500, Andrei Hurynovich wrote:
> Hi.
> 
> We are trying to build realtime(-ish) system based on rhel6(kernel 
> 2.6.32-642.1.1.el6.x86_64).
> 
> We used isolcpus to remove some cpus from process 
> scheduling(isolcpus=2-19 nohz_full=2-19 rcu_nocbs=2-19).
> 
> We spin off a program thread that set's its cpu affinity to one of
> those 
> isolated cpus, sets its scheduling chass to SCHED_FIFO, spins in a
> loop 
> and never sched_yield()-s to the kernel.
> 
> We set sysctl kernel.sched_rt_runtime_us = -1 so realtime threads
> are 
> NEVER interrupted.

You want an actual realtime kernel for that to work
right. The real time kernel currently supported by
Red Hat is 3.10 based, not 2.6.32 based.

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