The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/sched.c

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    1 /* 
    2  * Mach Operating System
    3  * Copyright (c) 1993-1987 Carnegie Mellon University
    4  * All Rights Reserved.
    5  * 
    6  * Permission to use, copy, modify and distribute this software and its
    7  * documentation is hereby granted, provided that both the copyright
    8  * notice and this permission notice appear in all copies of the
    9  * software, derivative works or modified versions, and any portions
   10  * thereof, and that both notices appear in supporting documentation.
   11  * 
   12  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
   13  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
   14  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
   15  * 
   16  * Carnegie Mellon requests users of this software to return to
   17  * 
   18  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
   19  *  School of Computer Science
   20  *  Carnegie Mellon University
   21  *  Pittsburgh PA 15213-3890
   22  * 
   23  * any improvements or extensions that they make and grant Carnegie Mellon
   24  * the rights to redistribute these changes.
   25  */
   26 /*
   27  * HISTORY
   28  * $Log:        sched.c,v $
   29  * Revision 2.2  93/11/17  17:20:51  dbg
   30  *      machparam.h -> machspl.h
   31  *      [93/05/21            dbg]
   32  * 
   33  *      Created file to hold routines for periodic scheduling
   34  *      calculations.
   35  *      [93/05/11            dbg]
   36  * 
   37  */ 
   38 
   39 #include <kern/clock.h>
   40 #include <kern/mach_timer.h>
   41 #include <kern/sched.h>
   42 
   43 #include <machine/machspl.h>
   44 
   45 /*
   46  *      sched_tick increments once a second.  Used to age priorities.
   47  */
   48 unsigned int    sched_tick = 0;
   49 
   50 #if     SIMPLE_CLOCK
   51 /*
   52  *      sched_usec is an exponential average of number of microseconds
   53  *      in a second for clock drift compensation.
   54  */
   55 
   56 int     sched_usec = 0;
   57 #endif  /* SIMPLE_CLOCK */
   58 
   59 extern void     compute_mach_factor(void);
   60 extern void     ts_thread_scan(void);
   61 
   62 /*
   63  *      sched_calculations:
   64  *
   65  *      Perform various periodic scheduling and statistics
   66  *      functions.  Runs off a periodic timer, at one-second
   67  *      intervals.
   68  */
   69 void sched_calculations(void)
   70 {
   71         /*
   72          *      Age usage one more second
   73          */
   74         sched_tick++;
   75 
   76 #if     SIMPLE_CLOCK
   77         /*
   78          *      Compensate for clock drift.  sched_usec is an
   79          *      exponential average of the number of microseconds in
   80          *      a second.  It decays in the same fashion as cpu_usage.
   81          */
   82         {
   83             int new_usec;
   84 
   85             new_usec = sched_usec_elapsed();
   86             sched_usec = (5*sched_usec + 3*new_usec)/8;
   87         }
   88 #endif  /* SIMPLE_CLOCK */
   89 
   90         /*
   91          *      Compute the load factors
   92          */
   93         compute_mach_factor();
   94 
   95         /*
   96          *      Raise the priorities of low-priority timesharing threads,
   97          *      every other second.
   98          */
   99         if (sched_tick & 1)
  100             ts_thread_scan();
  101 }
  102 
  103 /*
  104  *      Periodic timer for sched_calculations.
  105  */
  106 struct timer_elt        sched_timer;
  107 
  108 /*
  109  *      Initialize the timer.
  110  */
  111 void init_sched_calculations(void)
  112 {
  113         /*
  114          * Recalculate priorities once per second
  115          */
  116         sched_timer.te_fcn      = (void (*)(void *))sched_calculations;
  117         sched_timer.te_param    = 0;
  118         sched_timer.te_flags    = TELT_PERIODIC;
  119         sched_timer.te_period.seconds = 1;
  120         sched_timer.te_period.nanoseconds = 0;
  121         sched_timer.te_clock    = sys_clock;
  122 
  123         timer_elt_enqueue(&sched_timer, sched_timer.te_period, FALSE);
  124 }
  125 

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