Realtime Kernel

[nuta]

While achieving a truly realtime operating system will be a tough job, we might be able to implement some improvements on realtime-ness. This issue tracks ideas and the progress on the topic.

• Priority-based scheduling (see User-level scheduling #16)
• Stop disabling interrupts in the system call handler (and stop using Big Kernel Lock).
  • For lower latency in interrupt notification delivery to driver tasks.
• Add a build option to disallow page faults in the kernel's IPC path (especially in memcpy_from_user/memcpy_to_user).
  • Calling the pager task to handle the fault makes it difficult to analyze the worst-case execution time (WCET).
• WCET analysis (I'm not familiar with this. Needs your help!).