CS 3210 Design of Operating Systems
College of Computing, Georgia Tech

Lecture 10: Tuesday 15 February 2000

Processes, Threads, Scheduling: 

• Maxwell Ch 7
• Beck 3.1.3, 3.2.5, 3.3.3

announcements

• topic signups
• p3 progress? replacement Skiff board
• next week: Jamey Hicks, MIDTERM

process vs. thread vs. task 

quick scheduling review, preemption, timeslicing

"realtime"

priorities

• static (priority) [setpriority(), "niceness"] -- timeslice size (default 210ms?)
• dynamic (counter) -- timeslice counter in jiffies (counts down)
• realtime -- 0 for "normal", higher is better, only root

pids

• 0 .. 32767 (currently limited to 512)
• don't reuse "old" pids too quickly
• possible for processes to share PID! (clone stuff...)

data structures (picture from Maxwell Fig 7.2)

• pcb --> struct task_struct (1k!)
• excellent walk-through in Beck
• task (task array, process table)
• task list (prev_task, next_task)
• run queue (prev_run, next_run)
• pidhash (fast access via pid)
• task array freelist (tarray_freelist)
• "process graph"
  • original parent p_opptr ("reparenting")
  • current parent p_pptr
  • youngest child p_cptr
  • younger, older siblings p_ysptr, p_osptr

process states

• TASK_RUNNING (ready)
• TASK_INTERRUPTIBLE, TASK_UNINTERRUPTIBLE
• TASK_ZOMBIE
• TASK_STOPPED
• (TASK_SWAPPING)

fork, __clone

• cloning: CLONE_VM, _FS, _FILES, _SIGHAND, _PID
• copy-on-write
• kernel_thread? special kernel task, no preemption, for things like kswapd
• do_fork()
• "activating" a new process: wake_up_process(me) !

get_pid

• some tricks to return a "safe" unused pid
• maintains a "water mark"
• 300 !

exec

• setup some info "binprms"
• setup environment: args, env
• locate binary handler
• do_execve()

executable formats

• a.out, COFF, ELF, Java, "shells"
• ELF good support for dynamic linking, flexible
• magic numbers, #!
• "binary handler list"; search_binary_handler
• fs/binfmt_elf.c, _aout.c, _java.c, etc.
• table of function pointers (methods): load_binary, load_shlib, core_dump, etc.
• example: Java binary handler
  • load a JVM (what's *its* format? no recursion allowed!)

readings for next thursday (17 jan 2000)

• Maxwell Ch 7 scheduler proper