Practice Questions

1. Does Ubuntu use soft or hard modularity?

• Soft modularity
  • Voluntary, caller callee can mess with each other
• Hard modularity
  • More isolation
  • Caller, callee can’t mess with each other
  • Client server model, more cost of message passing
  • Virtualization
• Ubuntu uses virtualization for hard modularity
• Also uses soft modularity

1. Suppose x86 Xunil reverses pattern for sys calls—RETI instruction instead of INT

• Interrupt service vector
• Ecx, ebx, edx args. Eax syscall number. Interrupt 0x80.
• X86-64 uses new instructions to interrupt into kernel
• Could use this method—it’s a privileged instruction, so would work anyway

1. Round Two Robin, when quantum expires, might 0.5 chance to let current process run.

• Utilization: % of time doing useful work of T2R slightly higher (less context switches)
• Wait time: Roughly the same
• Response time: worse

1. Suppose compile some C program—what are the race conditions?

• Note: printf is not a sync safe, nor is the char n
• Output more than 256 lines? Interrupt after n++
• Successive lines of n=N: interrupt before n++