w/proc_compare.c

   1 /*-
   2  * Copyright (c) 1990, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 #include <sys/cdefs.h>
  35
  36 #ifndef lint
  37 static const char sccsid[] = "@(#)proc_compare.c        8.2 (Berkeley) 9/23/93";
  38 #endif
  39
  40 #include <sys/param.h>
  41 #include <sys/time.h>
  42 #include <sys/user.h>
  43
  44 #include "extern.h"
  45
  46 /*
  47  * Returns 1 if p2 is "better" than p1
  48  *
  49  * The algorithm for picking the "interesting" process is thus:
  50  *
  51  *      1) Only foreground processes are eligible - implied.
  52  *      2) Runnable processes are favored over anything else.  The runner
  53  *         with the highest cpu utilization is picked (p_estcpu).  Ties are
  54  *         broken by picking the highest pid.
  55  *      3) The sleeper with the shortest sleep time is next.  With ties,
  56  *         we pick out just "short-term" sleepers (PS_SINTR == 0).
  57  *      4) Further ties are broken by picking the highest pid.
  58  *
  59  * If you change this, be sure to consider making the change in the kernel
  60  * too (^T in kern/tty.c).
  61  *
  62  * TODO - consider whether pctcpu should be used.
  63  */
  64
  65 #include <sys/cdefs.h>
  66
  67
  68 #define ISRUN(p)        (((p)->p_stat == SRUN) || ((p)->p_stat == SIDL))
  69 #define TESTAB(a, b)    ((a)<<1 | (b))
  70 #define ONLYA   2
  71 #define ONLYB   1
  72 #define BOTH    3
  73
  74 int
  75 proc_compare(p1, p2)
  76         struct extern_proc *p1, *p2;
  77 {
  78
  79         if (p1 == NULL)
  80                 return (1);
  81         /*
  82          * see if at least one of them is runnable
  83          */
  84         switch (TESTAB(ISRUN(p1), ISRUN(p2))) {
  85         case ONLYA:
  86                 return (0);
  87         case ONLYB:
  88                 return (1);
  89         case BOTH:
  90                 /*
  91                  * tie - favor one with highest recent cpu utilization
  92                  */
  93                 if (p2->p_estcpu > p1->p_estcpu)
  94                         return (1);
  95                 if (p1->p_estcpu > p2->p_estcpu)
  96                         return (0);
  97                 return (p2->p_pid > p1->p_pid); /* tie - return highest pid */
  98         }
  99         /*
 100          * weed out zombies
 101          */
 102         switch (TESTAB(p1->p_stat == SZOMB, p2->p_stat == SZOMB)) {
 103         case ONLYA:
 104                 return (1);
 105         case ONLYB:
 106                 return (0);
 107         case BOTH:
 108                 return (p2->p_pid > p1->p_pid); /* tie - return highest pid */
 109         }
 110         /*
 111          * pick the one with the smallest sleep time
 112          */
 113         if (p2->p_slptime > p1->p_slptime)
 114                 return (0);
 115         if (p1->p_slptime > p2->p_slptime)
 116                 return (1);
 117         /*
 118          * favor one sleeping in a non-interruptible sleep
 119          */
 120         if (p1->p_flag & P_SINTR && (p2->p_flag & P_SINTR) == 0)
 121                 return (1);
 122         if (p2->p_flag & P_SINTR && (p1->p_flag & P_SINTR) == 0)
 123                 return (0);
 124         return (p2->p_pid > p1->p_pid); /* tie - return highest pid */
 125 }