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. We are observing that the program thread is indeed realtime and is never interrupted. After some time working like this, the system becomes irresponsive - ssh connections start failing with timeout, existing connections hang when trying to read/write to physical disks(reading procfs or writing to tmpfs is unaffected). *** According to /proc/sched_debug, it seems that kernel still schedules some SCHED_OTHER(e.g. non-realtime) kernel tasks to isolated cpus - for example cpu 18 get tasks events/18 and kblockd/18 that are stuck in runnable(but not running state), so those kernel processes never got a single time slice because our realtime process hogs 100% of cpu. And kernel/18 and kblockd/18 never migrate to other cpus because these tasks are pinned to cpu 18. *** Check please these /proc/sched_debug snapshots, you can see that events/18 and kblockd/18 sum-exec counters are not increasing: https://gist.github.com/altmind/5cf4aad87a4a082441c1ca9378a06154 The question is: Is it possible to never schedule kernel tasks on selected cpus? -- Thanks, Andrei Hurynovich