kernel/clock.c

   1 /* This file contains the clock task, which handles time related functions.
   2  * Important events that are handled by the CLOCK include setting and
   3  * monitoring alarm timers and deciding when to (re)schedule processes.
   4  * The CLOCK offers a direct interface to kernel processes. System services
   5  * can access its services through system calls, such as sys_setalarm(). The
   6  * CLOCK task thus is hidden from the outside world.
   7  *
   8  * Changes:
   9  *   Aug 18, 2006   removed direct hardware access etc, MinixPPC (Ingmar Alting)
  10  *   Oct 08, 2005   reordering and comment editing (A. S. Woodhull)
  11  *   Mar 18, 2004   clock interface moved to SYSTEM task (Jorrit N. Herder)
  12  *   Sep 30, 2004   source code documentation updated  (Jorrit N. Herder)
  13  *   Sep 24, 2004   redesigned alarm timers  (Jorrit N. Herder)
  14  *
  15  * Clock task is notified by the clock's interrupt handler when a timer
  16  * has expired.
  17  *
  18  * In addition to the main clock_task() entry point, which starts the main
  19  * loop, there are several other minor entry points:
  20  *   clock_stop:        called just before MINIX shutdown
  21  *   get_uptime:        get realtime since boot in clock ticks
  22  *   set_timer:         set a watchdog timer (+)
  23  *   reset_timer:       reset a watchdog timer (+)
  24  *   read_clock:        read the counter of channel 0 of the 8253A timer
  25  *
  26  * (+) The CLOCK task keeps tracks of watchdog timers for the entire kernel.
  27  * It is crucial that watchdog functions not block, or the CLOCK task may
  28  * be blocked. Do not send() a message when the receiver is not expecting it.
  29  * Instead, notify(), which always returns, should be used.
  30  */
  31
  32 #include "kernel.h"
  33 #include "proc.h"
  34 #include <minix/endpoint.h>
  35 #include <assert.h>
  36
  37 #include "clock.h"
  38 #include "debug.h"
  39
  40 #ifdef CONFIG_WATCHDOG
  41 #include "watchdog.h"
  42 #endif
  43
  44 /* Function prototype for PRIVATE functions.
  45  */
  46 FORWARD _PROTOTYPE( void load_update, (void));
  47
  48 /* The CLOCK's timers queue. The functions in <timers.h> operate on this.
  49  * Each system process possesses a single synchronous alarm timer. If other
  50  * kernel parts want to use additional timers, they must declare their own
  51  * persistent (static) timer structure, which can be passed to the clock
  52  * via (re)set_timer().
  53  * When a timer expires its watchdog function is run by the CLOCK task.
  54  */
  55 PRIVATE timer_t *clock_timers;  /* queue of CLOCK timers */
  56 PRIVATE clock_t next_timeout;   /* realtime that next timer expires */
  57
  58 /* The time is incremented by the interrupt handler on each clock tick.
  59  */
  60 PRIVATE clock_t realtime = 0;                 /* real time clock */
  61
  62 /*
  63  * The boot processor timer interrupt handler. In addition to non-boot cpus it
  64  * keeps real time and notifies the clock task if need be
  65  */
  66 PUBLIC int bsp_timer_int_handler(void)
  67 {
  68         unsigned ticks;
  69
  70         if(minix_panicing)
  71                 return 0;
  72
  73         /* Get number of ticks and update realtime. */
  74         ticks = lost_ticks + 1;
  75         lost_ticks = 0;
  76         realtime += ticks;
  77
  78         ap_timer_int_handler();
  79         assert(!proc_is_runnable(proc_ptr) || proc_ptr->p_ticks_left > 0);
  80
  81         /* if a timer expired, notify the clock task */
  82         if ((next_timeout <= realtime)) {
  83                 tmrs_exptimers(&clock_timers, realtime, NULL);
  84                 next_timeout = (clock_timers == NULL) ?
  85                         TMR_NEVER : clock_timers->tmr_exp_time;
  86         }
  87
  88         if (do_serial_debug)
  89                 do_ser_debug();
  90
  91         return(1);                                      /* reenable interrupts */
  92 }
  93
  94 /*===========================================================================*
  95  *                              get_uptime                                   *
  96  *===========================================================================*/
  97 PUBLIC clock_t get_uptime(void)
  98 {
  99   /* Get and return the current clock uptime in ticks. */
 100   return(realtime);
 101 }
 102
 103 /*===========================================================================*
 104  *                              set_timer                                    *
 105  *===========================================================================*/
 106 PUBLIC void set_timer(tp, exp_time, watchdog)
 107 struct timer *tp;               /* pointer to timer structure */
 108 clock_t exp_time;               /* expiration realtime */
 109 tmr_func_t watchdog;            /* watchdog to be called */
 110 {
 111 /* Insert the new timer in the active timers list. Always update the
 112  * next timeout time by setting it to the front of the active list.
 113  */
 114   tmrs_settimer(&clock_timers, tp, exp_time, watchdog, NULL);
 115   next_timeout = clock_timers->tmr_exp_time;
 116 }
 117
 118 /*===========================================================================*
 119  *                              reset_timer                                  *
 120  *===========================================================================*/
 121 PUBLIC void reset_timer(tp)
 122 struct timer *tp;               /* pointer to timer structure */
 123 {
 124 /* The timer pointed to by 'tp' is no longer needed. Remove it from both the
 125  * active and expired lists. Always update the next timeout time by setting
 126  * it to the front of the active list.
 127  */
 128   tmrs_clrtimer(&clock_timers, tp, NULL);
 129   next_timeout = (clock_timers == NULL) ?
 130         TMR_NEVER : clock_timers->tmr_exp_time;
 131 }
 132
 133 /*===========================================================================*
 134  *                              load_update                                  *
 135  *===========================================================================*/
 136 PRIVATE void load_update(void)
 137 {
 138         u16_t slot;
 139         int enqueued = 0, q;
 140         struct proc *p;
 141
 142         /* Load average data is stored as a list of numbers in a circular
 143          * buffer. Each slot accumulates _LOAD_UNIT_SECS of samples of
 144          * the number of runnable processes. Computations can then
 145          * be made of the load average over variable periods, in the
 146          * user library (see getloadavg(3)).
 147          */
 148         slot = (realtime / system_hz / _LOAD_UNIT_SECS) % _LOAD_HISTORY;
 149         if(slot != kloadinfo.proc_last_slot) {
 150                 kloadinfo.proc_load_history[slot] = 0;
 151                 kloadinfo.proc_last_slot = slot;
 152         }
 153
 154         /* Cumulation. How many processes are ready now? */
 155         for(q = 0; q < NR_SCHED_QUEUES; q++)
 156                 for(p = rdy_head[q]; p; p = p->p_nextready)
 157                         enqueued++;
 158
 159         kloadinfo.proc_load_history[slot] += enqueued;
 160
 161         /* Up-to-dateness. */
 162         kloadinfo.last_clock = realtime;
 163 }
 164
 165 /*
 166  * Timer interupt handler. This is the only thing executed on non boot
 167  * processors. It is called by bsp_timer_int_handler() on the boot processor
 168  */
 169 PUBLIC int ap_timer_int_handler(void)
 170 {
 171
 172         /* Update user and system accounting times. Charge the current process
 173          * for user time. If the current process is not billable, that is, if a
 174          * non-user process is running, charge the billable process for system
 175          * time as well.  Thus the unbillable process' user time is the billable
 176          * user's system time.
 177          */
 178
 179         const unsigned ticks = 1;
 180         struct proc * p, * billp;
 181
 182 #ifdef CONFIG_WATCHDOG
 183         /*
 184          * we need to know whether local timer ticks are happening or whether
 185          * the kernel is locked up. We don't care about overflows as we only
 186          * need to know that it's still ticking or not
 187          */
 188         watchdog_local_timer_ticks++;
 189 #endif
 190
 191         /* Update user and system accounting times. Charge the current process
 192          * for user time. If the current process is not billable, that is, if a
 193          * non-user process is running, charge the billable process for system
 194          * time as well.  Thus the unbillable process' user time is the billable
 195          * user's system time.
 196          */
 197
 198         /* FIXME prepared for get_cpu_local_var() */
 199         p = proc_ptr;
 200         billp = bill_ptr;
 201
 202         p->p_user_time += ticks;
 203
 204 #if DEBUG_RACE
 205         /* With DEBUG_RACE, every process gets interrupted. */
 206         p->p_ticks_left = 0;
 207 #else
 208         if (priv(p)->s_flags & PREEMPTIBLE) {
 209                 p->p_ticks_left -= ticks;
 210         }
 211 #endif
 212         if (! (priv(p)->s_flags & BILLABLE)) {
 213                 billp->p_sys_time += ticks;
 214         }
 215
 216         /* Decrement virtual timers, if applicable. We decrement both the
 217          * virtual and the profile timer of the current process, and if the
 218          * current process is not billable, the timer of the billed process as
 219          * well.  If any of the timers expire, do_clocktick() will send out
 220          * signals.
 221          */
 222         if ((p->p_misc_flags & MF_VIRT_TIMER)){
 223                 p->p_virt_left -= ticks;
 224         }
 225         if ((p->p_misc_flags & MF_PROF_TIMER)){
 226                 p->p_prof_left -= ticks;
 227         }
 228         if (! (priv(p)->s_flags & BILLABLE) &&
 229                         (billp->p_misc_flags & MF_PROF_TIMER)){
 230                 billp->p_prof_left -= ticks;
 231         }
 232
 233         /*
 234          * Check if a process-virtual timer expired. Check current process, but
 235          * also bill_ptr - one process's user time is another's system time, and
 236          * the profile timer decreases for both!
 237          */
 238         vtimer_check(p);
 239
 240         if (p != billp)
 241                 vtimer_check(billp);
 242
 243         /* Update load average. */
 244         load_update();
 245
 246         /* check if the processes still have some ticks left */
 247         check_ticks_left(p);
 248
 249         return 1;
 250 }
 251
 252 PUBLIC int boot_cpu_init_timer(unsigned freq)
 253 {
 254         if (arch_init_local_timer(freq))
 255                 return -1;
 256
 257         if (arch_register_local_timer_handler(
 258                                 (irq_handler_t) bsp_timer_int_handler))
 259                 return -1;
 260
 261         return 0;
 262 }