text: // Per-CPU state
  struct cpu {
    uchar apicid;                // Local APIC ID
    struct context *scheduler;   // swtch() here to enter scheduler
    struct taskstate ts;         // Used by x86 to find stack for interrupt
    struct segdesc gdt[NSEGS];   // x86 global descriptor table
    volatile uint started;       // Has the CPU started?
    int ncli;                    // Depth of pushcli nesting.
    int intena;                  // Were interrupts enabled before pushcli?
    struct proc *proc;           // The process running on this cpu or null
  };
  
  extern struct cpu cpus[NCPU];
  extern int ncpu;
  
  //PAGEBREAK: 17
  // Saved registers for kernel context switches.
  // Don't need to save all the segment registers (%cs, etc),
  // because they are constant across kernel contexts.
  // Don't need to save %eax, %ecx, %edx, because the
  // x86 convention is that the caller has saved them.
  // Contexts are stored at the bottom of the stack they
  // describe; the stack pointer is the address of the context.
  // The layout of the context matches the layout of the stack in swtch.S
  // at the "Switch stacks" comment. Switch doesn't save eip explicitly,
  // but it is on the stack and allocproc() manipulates it.
  struct context {
    uint edi;
    uint esi;
    uint ebx;
    uint ebp;
    uint eip;
  };
  
  enum procstate { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };
  
  // Per-process state
  struct proc {
    uint sz;                     // Size of process memory (bytes)
    pde_t* pgdir;                // Page table
    char *kstack;                // Bottom of kernel stack for this process
    enum procstate state;        // Process state
    int pid;                     // Process ID
    struct proc *parent;         // Parent process
    struct trapframe *tf;        // Trap frame for current syscall
    struct context *context;     // swtch() here to run process
    void *chan;                  // If non-zero, sleeping on chan
    int killed;                  // If non-zero, have been killed
    struct file *ofile[NOFILE];  // Open files
    struct inode *cwd;           // Current directory
    char name[16];               // Process name (debugging)
    int threads;
    int stackTop;
    int status;
  
    // int rrRemainingTime; // Remaining time left for RR scheduling
    int priority;       // Process priority, 1 highest, 6 lowest.
  
    int creationTime;    // Time which this process was created 
    int sleepingTime;    // Time spent being in SLEEPING state
    int runnableTime;    // Time spent being in RUNNABLE state
    int runningTime;     // Time spent being in RUNNING state
    int terminationTime; // Time which this process was terminated 
  
    int queue;                  // Defines in which queue the process belongs
  
  
  };
  
  // Scheduling options
  enum schedPolicy
  {
    DEFAULT = 0,
    ROUND_ROBIN = 1,
    PRIORITY = 2,
    MULTILAYRED_PRIORITY = 3,
    DYNAMIC_MULTILAYER_PRIOITY=4
  };
  
  extern enum schedPolicy policy;
  
  
  // Process memory is laid out contiguously, low addresses first:
  //   text
  //   original data and bss
  //   fixed-size stack
  //   expandable heap
  