proc_compare.c revision 1591 
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#ifndef lint
35static char sccsid[] = "@(#)proc_compare.c	8.2 (Berkeley) 9/23/93";
36#endif /* not lint */
37
38#include <sys/param.h>
39#include <sys/time.h>
40#include <sys/proc.h>
41
42#include "extern.h"
43
44/*
45 * Returns 1 if p2 is "better" than p1
46 *
47 * The algorithm for picking the "interesting" process is thus:
48 *
49 *	1) Only foreground processes are eligible - implied.
50 *	2) Runnable processes are favored over anything else.  The runner
51 *	   with the highest cpu utilization is picked (p_estcpu).  Ties are
52 *	   broken by picking the highest pid.
53 *	3) The sleeper with the shortest sleep time is next.  With ties,
54 *	   we pick out just "short-term" sleepers (P_SINTR == 0).
55 *	4) Further ties are broken by picking the highest pid.
56 *
57 * If you change this, be sure to consider making the change in the kernel
58 * too (^T in kern/tty.c).
59 *
60 * TODO - consider whether pctcpu should be used.
61 */
62
63#define ISRUN(p)	(((p)->p_stat == SRUN) || ((p)->p_stat == SIDL))
64#define TESTAB(a, b)    ((a)<<1 | (b))
65#define ONLYA   2
66#define ONLYB   1
67#define BOTH    3
68
69int
70proc_compare(p1, p2)
71	register struct proc *p1, *p2;
72{
73
74	if (p1 == NULL)
75		return (1);
76	/*
77	 * see if at least one of them is runnable
78	 */
79	switch (TESTAB(ISRUN(p1), ISRUN(p2))) {
80	case ONLYA:
81		return (0);
82	case ONLYB:
83		return (1);
84	case BOTH:
85		/*
86		 * tie - favor one with highest recent cpu utilization
87		 */
88		if (p2->p_estcpu > p1->p_estcpu)
89			return (1);
90		if (p1->p_estcpu > p2->p_estcpu)
91			return (0);
92		return (p2->p_pid > p1->p_pid);	/* tie - return highest pid */
93	}
94	/*
95 	 * weed out zombies
96	 */
97	switch (TESTAB(p1->p_stat == SZOMB, p2->p_stat == SZOMB)) {
98	case ONLYA:
99		return (1);
100	case ONLYB:
101		return (0);
102	case BOTH:
103		return (p2->p_pid > p1->p_pid); /* tie - return highest pid */
104	}
105	/*
106	 * pick the one with the smallest sleep time
107	 */
108	if (p2->p_slptime > p1->p_slptime)
109		return (0);
110	if (p1->p_slptime > p2->p_slptime)
111		return (1);
112	/*
113	 * favor one sleeping in a non-interruptible sleep
114	 */
115	if (p1->p_flag & P_SINTR && (p2->p_flag & P_SINTR) == 0)
116		return (1);
117	if (p2->p_flag & P_SINTR && (p1->p_flag & P_SINTR) == 0)
118		return (0);
119	return (p2->p_pid > p1->p_pid);		/* tie - return highest pid */
120}
121