1. Process & CFS

2. Process

3. Process Program in the midst of execution How to create new process fork(), vfork() exec()

4. Data structure task_struct Process descriptor http://lxr.linux.no/linux+v2.6.39/include/linux/sched.h#L1193 Priority(prio, static_prio, normal_prio) Scheduling class(sched_class) Scheduling policy(policy) Link parent, child, sibling, group_leader

5. Data structure thread_infohttp://lxr.linux.no/linux+v2.6.39/arch/arm/include/asm/thread_info.h#L50 Describe process data accessed by architecture specific code Difference among other CPUs Managed information task_struct flags for scheduling(TIF_SIGPANDING, TIF_NEED_RESCHED) cpu number (for multi processor) preempt_count

6. Data structure thread_unionhttp://lxr.linux.no/linux+v2.6.39/include/linux/sched.h#L2011 Kernel stack & thread_info 1 or 2 pages(8KB) Kernel stack size is less then 8K

7. Process states

8. Process creation system call fork() Duplicate of the parent's page tables Create unique process descriptor for child(pidetc) Copy-on-Write Delay the copying pages exec() is called right after fork() vfork() Same as fork() except copying of parent page table Share parent's address space Child first scheme Parent is blocked until the child calls exec() or exits

9. do_fork() Start point of fork

10. copy_process()

11. Thread Implementation threads as same as standard processes One thread has own task_struct pid/ tgid Create clone() system call clone(CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND, 0); clone(SIGCHLD, 0); // fork() clone(CLONE_VFORK | CLONE_VM | SIGCHLD, 0); // vfork()

12. Kernel Threads Standard processes running in kernel space Do not have an address space(task_struct.mm is NULL) Schedulable, preemptable like normal process kthread_create() for creation

13. Process Termination exit() wait(), waitpid()

14. Scheduling

15. Scheduling CoopreativevsPreemptive yield timeslice IO bound vs CPU bound Low latency vsHigh throughput

16. Process priority nice Integer value(-20~19, default 0) High nice value correspond to low priority renice, setpriority() Realtime priority Always higher priority than normal processes Integer value(0~99)

17. Process priority Priority kernel internal Integer value (0~139) nice values[-20~19] are map to [100~139] [0~99] for realtime processes

18. Fairness scheduling RR on static timeslice 100ms(0 nice) vs 95ms(1 nice) 10ms(19 nice) vs 5ms (20 nice) A user’s 100 processes vs B user’s 1process Per user based scheduling Enable when kernel build Per thread level scheduling One nice value down gets 10% more CPU power vruntime(virtual clock) Support CGroupscheduling http://www.mjmwired.net/kernel/Documentation/scheduler/sched-design-CFS.txt

19. Overview schedule() Core T T T Ruequene do_fork() wake_up_new_task() T Tß T Waitqueue Core T Ruequene Core T T Ruequene Core T T Ruequene

20. tast_struct sched_class seched_entity sched_class Sched_entity load_weight on_rq vruntime rq load_weight cfs_rq rt_rq load_weight

21. CFS policy Soft real-time policy Posix standard Priority scheduling One nice level down gets 10% more CPU power Virtual clock Conceptual time considering priority Task waiting most of time will be scheduled to run Time order is managed by Runqueue

22. Data struct task_struct http://lxr.linux.no/linux+v2.6.39/include/linux/sched.h#L1193 SCHED_NORMAL SCHED_BATCH SCHED_IDLE SCHED_FIFO SCHED_RR

23. Data struct sched_class http://lxr.linux.no/linux+v2.6.39/include/linux/sched.h#L1056

24. Data struct rq http://lxr.linux.no/linux+v2.6.39/kernel/sched.c#L447

25. Data struct sched_entity http://lxr.linux.no/linux+v2.6.39/include/linux/sched.h#L1142

26. Dealing with priority Basic static_prio Value inherited by parent or set prio,normal_prio Dynamically changed

27. Dealing with priority Code

28. Computing Load weights load_weight

29. Remaining How to determine vruntime Process selection When schedule() function is called Context switching Sleep and Wake up Cgroup Hard to understand