w/proc_compare.c

   1 /*      $NetBSD: proc_compare.c,v 1.7 1997/10/20 02:49:14 mrg Exp $     */
   2
   3 /*-
   4  * Copyright (c) 1990, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. All advertising materials mentioning features or use of this software
  16  *    must display the following acknowledgement:
  17  *      This product includes software developed by the University of
  18  *      California, Berkeley and its contributors.
  19  * 4. Neither the name of the University nor the names of its contributors
  20  *    may be used to endorse or promote products derived from this software
  21  *    without specific prior written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  33  * SUCH DAMAGE.
  34  */
  35
  36 #include <sys/cdefs.h>
  37 #ifndef lint
  38 #if 0
  39 static char sccsid[] = "@(#)proc_compare.c      8.2 (Berkeley) 9/23/93";
  40 #else
  41 __RCSID("$NetBSD: proc_compare.c,v 1.7 1997/10/20 02:49:14 mrg Exp $");
  42 #endif
  43 #endif /* not lint */
  44
  45 #include <sys/param.h>
  46 #include <sys/time.h>
  47 #include <sys/proc.h>
  48
  49 #include "extern.h"
  50
  51 /*
  52  * Returns 1 if p2 is "better" than p1
  53  *
  54  * The algorithm for picking the "interesting" process is thus:
  55  *
  56  *      1) Only foreground processes are eligible - implied.
  57  *      2) Runnable processes are favored over anything else.  The runner
  58  *         with the highest cpu utilization is picked (p_estcpu).  Ties are
  59  *         broken by picking the highest pid.
  60  *      3) The sleeper with the shortest sleep time is next.  With ties,
  61  *         we pick out just "short-term" sleepers (P_SINTR == 0).
  62  *      4) Further ties are broken by picking the highest pid.
  63  *
  64  * If you change this, be sure to consider making the change in the kernel
  65  * too (^T in kern/tty.c).
  66  *
  67  * TODO - consider whether pctcpu should be used.
  68  */
  69
  70 #define ISRUN(p)        (((p)->p_stat == SRUN) || ((p)->p_stat == SIDL))
  71 #define TESTAB(a, b)    ((a)<<1 | (b))
  72 #define ONLYA   2
  73 #define ONLYB   1
  74 #define BOTH    3
  75
  76 int
  77 proc_compare(p1, p2)
  78         struct proc *p1, *p2;
  79 {
  80
  81         if (p1 == NULL)
  82                 return (1);
  83         /*
  84          * see if at least one of them is runnable
  85          */
  86         switch (TESTAB(ISRUN(p1), ISRUN(p2))) {
  87         case ONLYA:
  88                 return (0);
  89         case ONLYB:
  90                 return (1);
  91         case BOTH:
  92                 /*
  93                  * tie - favor one with highest recent cpu utilization
  94                  */
  95                 if (p2->p_estcpu > p1->p_estcpu)
  96                         return (1);
  97                 if (p1->p_estcpu > p2->p_estcpu)
  98                         return (0);
  99                 return (p2->p_pid > p1->p_pid); /* tie - return highest pid */
 100         }
 101         /*
 102          * weed out zombies
 103          */
 104         switch (TESTAB(p1->p_stat == SZOMB, p2->p_stat == SZOMB)) {
 105         case ONLYA:
 106                 return (1);
 107         case ONLYB:
 108                 return (0);
 109         case BOTH:
 110                 return (p2->p_pid > p1->p_pid); /* tie - return highest pid */
 111         }
 112         /*
 113          * pick the one with the smallest sleep time
 114          */
 115         if (p2->p_slptime > p1->p_slptime)
 116                 return (0);
 117         if (p1->p_slptime > p2->p_slptime)
 118                 return (1);
 119         /*
 120          * favor one sleeping in a non-interruptible sleep
 121          */
 122         if (p1->p_flag & P_SINTR && (p2->p_flag & P_SINTR) == 0)
 123                 return (1);
 124         if (p2->p_flag & P_SINTR && (p1->p_flag & P_SINTR) == 0)
 125                 return (0);
 126         return (p2->p_pid > p1->p_pid);         /* tie - return highest pid */
 127 }