xref: /freebsd/usr.bin/w/proc_compare.c (revision 5b31cc94b10d4bb7109c6b27940a0fc76a44a331)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
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. Neither the name of the University nor the names of its contributors
16  *    may be used to endorse or promote products derived from this software
17  *    without specific prior written permission.
18  *
19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29  * SUCH DAMAGE.
30  */
31 
32 #if 0
33 #endif
34 
35 #include <sys/cdefs.h>
36 #include <sys/param.h>
37 #include <sys/proc.h>
38 #include <sys/time.h>
39 #include <sys/user.h>
40 
41 #include "extern.h"
42 
43 /*
44  * Returns 1 if p2 is "better" than p1
45  *
46  * The algorithm for picking the "interesting" process is thus:
47  *
48  *	1) Only foreground processes are eligible - implied.
49  *	2) Runnable processes are favored over anything else.  The runner
50  *	   with the highest cpu utilization is picked (p_estcpu).  Ties are
51  *	   broken by picking the highest pid.
52  *	3) The sleeper with the shortest sleep time is next.  With ties,
53  *	   we pick out just "short-term" sleepers (TDF_SINTR == 0).
54  *	4) Further ties are broken by picking the highest pid.
55  *
56  * If you change this, be sure to consider making the change in the kernel
57  * too (^T in kern/tty.c).
58  *
59  * TODO - consider whether pctcpu should be used.
60  */
61 
62 #define	ISRUN(p)	(((p)->ki_stat == SRUN) || ((p)->ki_stat == SIDL))
63 #define	TESTAB(a, b)    ((a)<<1 | (b))
64 #define	ONLYA   2
65 #define	ONLYB   1
66 #define	BOTH    3
67 
68 int
69 proc_compare(struct kinfo_proc *p1, struct kinfo_proc *p2)
70 {
71 
72 	if (p1 == NULL)
73 		return (1);
74 	/*
75 	 * see if at least one of them is runnable
76 	 */
77 	switch (TESTAB(ISRUN(p1), ISRUN(p2))) {
78 	case ONLYA:
79 		return (0);
80 	case ONLYB:
81 		return (1);
82 	case BOTH:
83 		/*
84 		 * tie - favor one with highest recent cpu utilization
85 		 */
86 		if (p2->ki_estcpu > p1->ki_estcpu)
87 			return (1);
88 		if (p1->ki_estcpu > p2->ki_estcpu)
89 			return (0);
90 		return (p2->ki_pid > p1->ki_pid); /* tie - return highest pid */
91 	}
92 	/*
93 	 * weed out zombies
94 	 */
95 	switch (TESTAB(p1->ki_stat == SZOMB, p2->ki_stat == SZOMB)) {
96 	case ONLYA:
97 		return (1);
98 	case ONLYB:
99 		return (0);
100 	case BOTH:
101 		return (p2->ki_pid > p1->ki_pid); /* tie - return highest pid */
102 	}
103 	/*
104 	 * pick the one with the smallest sleep time
105 	 */
106 	if (p2->ki_slptime > p1->ki_slptime)
107 		return (0);
108 	if (p1->ki_slptime > p2->ki_slptime)
109 		return (1);
110 	/*
111 	 * favor one sleeping in a non-interruptible sleep
112 	 */
113 	if (p1->ki_tdflags & TDF_SINTR && (p2->ki_tdflags & TDF_SINTR) == 0)
114 		return (1);
115 	if (p2->ki_tdflags & TDF_SINTR && (p1->ki_tdflags & TDF_SINTR) == 0)
116 		return (0);
117 	return (p2->ki_pid > p1->ki_pid);	/* tie - return highest pid */
118 }
119