Usually with real time OSes in my experience on Linux (preempt rt), throughput performance tends to drop a bit because now the processor is responding to inputs ASAP and so other tasks need to wait. Inputs can be network/file I/O, and user inputs.

If the processor is rendering a frame and a network packet comes in, now it needs to respond to the network first, and render the frame after processing the packet. That is a very simplified example on one processor, but there are trade-offs depending on workload/inputs/context-switching is what I'm saying, and measuring latency is step one in trying to optimize for it.