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 <minix/endpoint.h>
  34 #include <assert.h>
  35
  36 #include "clock.h"
  37
  38 #ifdef USE_WATCHDOG
  39 #include "watchdog.h"
  40 #endif
  41
  42 /* Function prototype for PRIVATE functions.
  43  */
  44 static void load_update(void);
  45
  46 /* The CLOCK's timers queue. The functions in <timers.h> operate on this.
  47  * Each system process possesses a single synchronous alarm timer. If other
  48  * kernel parts want to use additional timers, they must declare their own
  49  * persistent (static) timer structure, which can be passed to the clock
  50  * via (re)set_timer().
  51  * When a timer expires its watchdog function is run by the CLOCK task.
  52  */
  53 static timer_t *clock_timers;   /* queue of CLOCK timers */
  54 static clock_t next_timeout;    /* realtime that next timer expires */
  55
  56 /* The time is incremented by the interrupt handler on each clock tick.
  57  */
  58 static clock_t realtime = 0;                  /* real time clock */
  59
  60 /*
  61  * The boot processos timer interrupt handler. In addition to non-boot cpus it
  62  * keeps real time and notifies the clock task if need be
  63  */
  64 int timer_int_handler(void)
  65 {
  66         /* Update user and system accounting times. Charge the current process
  67          * for user time. If the current process is not billable, that is, if a
  68          * non-user process is running, charge the billable process for system
  69          * time as well.  Thus the unbillable process' user time is the billable
  70          * user's system time.
  71          */
  72
  73         struct proc * p, * billp;
  74
  75         /* FIXME watchdog for slave cpus! */
  76 #ifdef USE_WATCHDOG
  77         /*
  78          * we need to know whether local timer ticks are happening or whether
  79          * the kernel is locked up. We don't care about overflows as we only
  80          * need to know that it's still ticking or not
  81          */
  82         watchdog_local_timer_ticks++;
  83 #endif
  84
  85         if (cpu_is_bsp(cpuid))
  86                 realtime++;
  87
  88         /* Update user and system accounting times. Charge the current process
  89          * for user time. If the current process is not billable, that is, if a
  90          * non-user process is running, charge the billable process for system
  91          * time as well.  Thus the unbillable process' user time is the billable
  92          * user's system time.
  93          */
  94
  95         p = get_cpulocal_var(proc_ptr);
  96         billp = get_cpulocal_var(bill_ptr);
  97
  98         p->p_user_time++;
  99
 100         if (! (priv(p)->s_flags & BILLABLE)) {
 101                 billp->p_sys_time++;
 102         }
 103
 104         /* Decrement virtual timers, if applicable. We decrement both the
 105          * virtual and the profile timer of the current process, and if the
 106          * current process is not billable, the timer of the billed process as
 107          * well.  If any of the timers expire, do_clocktick() will send out
 108          * signals.
 109          */
 110         if ((p->p_misc_flags & MF_VIRT_TIMER)){
 111                 p->p_virt_left--;
 112         }
 113         if ((p->p_misc_flags & MF_PROF_TIMER)){
 114                 p->p_prof_left--;
 115         }
 116         if (! (priv(p)->s_flags & BILLABLE) &&
 117                         (billp->p_misc_flags & MF_PROF_TIMER)){
 118                 billp->p_prof_left--;
 119         }
 120
 121         /*
 122          * Check if a process-virtual timer expired. Check current process, but
 123          * also bill_ptr - one process's user time is another's system time, and
 124          * the profile timer decreases for both!
 125          */
 126         vtimer_check(p);
 127
 128         if (p != billp)
 129                 vtimer_check(billp);
 130
 131         /* Update load average. */
 132         load_update();
 133
 134         if (cpu_is_bsp(cpuid)) {
 135                 /* if a timer expired, notify the clock task */
 136                 if ((next_timeout <= realtime)) {
 137                         tmrs_exptimers(&clock_timers, realtime, NULL);
 138                         next_timeout = (clock_timers == NULL) ?
 139                                 TMR_NEVER : clock_timers->tmr_exp_time;
 140                 }
 141
 142 #ifdef DEBUG_SERIAL
 143                 if (kinfo.do_serial_debug)
 144                         do_ser_debug();
 145 #endif
 146
 147         }
 148
 149         arch_timer_int_handler();
 150
 151         return(1);                                      /* reenable interrupts */
 152 }
 153
 154 /*===========================================================================*
 155  *                              get_uptime                                   *
 156  *===========================================================================*/
 157 clock_t get_uptime(void)
 158 {
 159   /* Get and return the current clock uptime in ticks. */
 160   return(realtime);
 161 }
 162
 163 /*===========================================================================*
 164  *                              set_timer                                    *
 165  *===========================================================================*/
 166 void set_timer(tp, exp_time, watchdog)
 167 struct timer *tp;               /* pointer to timer structure */
 168 clock_t exp_time;               /* expiration realtime */
 169 tmr_func_t watchdog;            /* watchdog to be called */
 170 {
 171 /* Insert the new timer in the active timers list. Always update the
 172  * next timeout time by setting it to the front of the active list.
 173  */
 174   tmrs_settimer(&clock_timers, tp, exp_time, watchdog, NULL);
 175   next_timeout = clock_timers->tmr_exp_time;
 176 }
 177
 178 /*===========================================================================*
 179  *                              reset_timer                                  *
 180  *===========================================================================*/
 181 void reset_timer(tp)
 182 struct timer *tp;               /* pointer to timer structure */
 183 {
 184 /* The timer pointed to by 'tp' is no longer needed. Remove it from both the
 185  * active and expired lists. Always update the next timeout time by setting
 186  * it to the front of the active list.
 187  */
 188   tmrs_clrtimer(&clock_timers, tp, NULL);
 189   next_timeout = (clock_timers == NULL) ?
 190         TMR_NEVER : clock_timers->tmr_exp_time;
 191 }
 192
 193 /*===========================================================================*
 194  *                              load_update                                  *
 195  *===========================================================================*/
 196 static void load_update(void)
 197 {
 198         u16_t slot;
 199         int enqueued = 0, q;
 200         struct proc *p;
 201         struct proc **rdy_head;
 202
 203         /* Load average data is stored as a list of numbers in a circular
 204          * buffer. Each slot accumulates _LOAD_UNIT_SECS of samples of
 205          * the number of runnable processes. Computations can then
 206          * be made of the load average over variable periods, in the
 207          * user library (see getloadavg(3)).
 208          */
 209         slot = (realtime / system_hz / _LOAD_UNIT_SECS) % _LOAD_HISTORY;
 210         if(slot != kloadinfo.proc_last_slot) {
 211                 kloadinfo.proc_load_history[slot] = 0;
 212                 kloadinfo.proc_last_slot = slot;
 213         }
 214
 215         rdy_head = get_cpulocal_var(run_q_head);
 216         /* Cumulation. How many processes are ready now? */
 217         for(q = 0; q < NR_SCHED_QUEUES; q++) {
 218                 for(p = rdy_head[q]; p != NULL; p = p->p_nextready) {
 219                         enqueued++;
 220                 }
 221         }
 222
 223         kloadinfo.proc_load_history[slot] += enqueued;
 224
 225         /* Up-to-dateness. */
 226         kloadinfo.last_clock = realtime;
 227 }
 228
 229 int boot_cpu_init_timer(unsigned freq)
 230 {
 231         if (init_local_timer(freq))
 232                 return -1;
 233
 234         if (register_local_timer_handler(
 235                                 (irq_handler_t) timer_int_handler))
 236                 return -1;
 237
 238         return 0;
 239 }
 240
 241 int app_cpu_init_timer(unsigned freq)
 242 {
 243         if (init_local_timer(freq))
 244                 return -1;
 245
 246         return 0;
 247 }