Monday, August 5, 2013

[TALK] Exokernel VS. Microkernel/

  • I presented the topic "Exokernel VS. Microkernel" at Taiwan COSCUP 2013 with about 1500 attendees.  I focus on Exokernel design and its implementation to show some differences from Microkernel.
  • Something through this presentation I want to convey sincerely is that 
    1. Ambitious app designers could design OS services just for its own applications to achieve better performance and optimization.
    2. By Exokernel design and principle, ambitious app designers could release their creative soul to customize almost all OS services they want.
  • I enjoy discussing, learning, and implementing system topics like OS kernels, virtualization, and embedded products,  mobile application, etc.

Saturday, April 27, 2013

Lab4 Preemptive Multitasking

[Preface] A Hope That My Crude Remarks May Draw Forth By Abler People

GitHub: MIT-6.828-Adventure-Lab4

  • Part A: Multiprocessor Support and Cooperative Multitasking.
    • Initialize hardware support.
      • Main goal: Make every CPUs have its own independent data.
      • Booting CPU triggers the bootaps() to set up each CPU by env_init_percpu() through mpentry.S to call mp_main().
      • ma_main() triggers
        • env_init_percpu
          • trap_init_percpu() setup each CPU's own TSS and stack allocated from mem_init_mp()
            • ltr(tss)
            • lidt
        • trap_init_percpu()
          • setup es/ds/fs/gs/fs/ss
          • setup CS by ljmp
    • Big Kernel Lock setup to ensure only one trap to capable to enter the kernel mode in the same time between all CPUs.
    • Implement Round-Robin scheduling.
  • Part B: Copy-on-Write Fork. 
    • I must say this part is very very interesting!!!
      • user mode page fault handler
      • The translation between UXSTACK, Kernel stack, and normal user stack.
    • The guide on Lab4 is very very detailed, I hope U could enjoy this part!
    • Note: Difference between faultalloc.c and faultallocbad.c
      • faultallocbad.c trigger user_mem_assert under kernel mode, so it can't print out.
      • faultalloc.c trigger 3 times page fault under user mode
        • 1 by deadbeef printing.
        • 2 by cafebffe printing.(contains recursive page fault)
  • Part C: Preemptive Multitasking and Inter-Process communication (IPC).
    • Avoid one user process keep occupying CPU if it likes.
    • Enable timer interrupt as the Force in Jedi to make Process release CPU.
    • IPC here is applied in Blocking Send and Blocking Receive.
      • It could be used as the basic lock mechanism, too.
    • This part could be the Integration system test for lab 1~4, for interactions between kernel and users. :)
  • Some questions assignment after exercises.