User-space partitioning, core isolation, NO_HZ_FULL

Dual-OS partitioning, using a POSIX RTOS in some cores, over a hypervisor

https://yosh.ke.mu/raspberry_pi_isolating_cores_in_linux_kernel

In user space:

• Process (fork)
• Thread (pthread_create)

In kernel:

• Kernel thread (kthreadd)

sched_class stop > dl > rt > cfs > idle (e.g. rt threads will run with higher priority than cfs threads) (stop and idle scheduling class are not accessible for user space applications)

rt includes SCHED_FIFO and SCHED_RR policies.

dl includes SCHED_DEADLINE policy (augmented EDF).

• chrt
• taskset

• sched_setattr
• sched_setaffinity
• CPU_SET
• pthread_setaffinity_np

• sched_setscheduler
• …

Latency measurement with cyclictest (results for SCHED_FIFO).

Sources of latency:

• Kernel system call
• ISR
• Kernel locks
• Priority inversions
• Timers
• Page faults

Ftrace

Kernel Shark

LLTng