Are all system calls non-realtime-safe?

Question

I've heard that executing system calls in Linux (RT_PREEMPT kernel) is never realtime-safe.

This seems overly-restrictive -- how could your process do anything (unless it has to be done entirely through DMA) without system calls?

Is this true, or are some system calls (like clock_gettime) realtime-safe?

Answer 1

If by "realtime safe" you mean guaranteed to execute within a bounded time, then linux, like most general-purpose operating systems, is not realtime safe.

Various real-time operating systems (RTOS) provided this kind of guarantee.