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#include <sys/param.h>
33#include <sys/proc.h>
34#include <sys/time.h>
35#include <sys/user.h>
36
37#include "extern.h"
38
39/*
40 * Returns 1 if p2 is "better" than p1
41 *
42 * The algorithm for picking the "interesting" process is thus:
43 *
44 *	1) Only foreground processes are eligible - implied.
45 *	2) Runnable processes are favored over anything else.  The runner
46 *	   with the highest cpu utilization is picked (p_estcpu).  Ties are
47 *	   broken by picking the highest pid.
48 *	3) The sleeper with the shortest sleep time is next.  With ties,
49 *	   we pick out just "short-term" sleepers (TDF_SINTR == 0).
50 *	4) Further ties are broken by picking the highest pid.
51 *
52 * If you change this, be sure to consider making the change in the kernel
53 * too (^T in kern/tty.c).
54 *
55 * TODO - consider whether pctcpu should be used.
56 */
57
58#define	ISRUN(p)	(((p)->ki_stat == SRUN) || ((p)->ki_stat == SIDL))
59#define	TESTAB(a, b)    ((a)<<1 | (b))
60#define	ONLYA   2
61#define	ONLYB   1
62#define	BOTH    3
63
64int
65proc_compare(struct kinfo_proc *p1, struct kinfo_proc *p2)
66{
67
68	if (p1 == NULL)
69		return (1);
70	/*
71	 * see if at least one of them is runnable
72	 */
73	switch (TESTAB(ISRUN(p1), ISRUN(p2))) {
74	case ONLYA:
75		return (0);
76	case ONLYB:
77		return (1);
78	case BOTH:
79		/*
80		 * tie - favor one with highest recent cpu utilization
81		 */
82		if (p2->ki_estcpu > p1->ki_estcpu)
83			return (1);
84		if (p1->ki_estcpu > p2->ki_estcpu)
85			return (0);
86		return (p2->ki_pid > p1->ki_pid); /* tie - return highest pid */
87	}
88	/*
89	 * weed out zombies
90	 */
91	switch (TESTAB(p1->ki_stat == SZOMB, p2->ki_stat == SZOMB)) {
92	case ONLYA:
93		return (1);
94	case ONLYB:
95		return (0);
96	case BOTH:
97		return (p2->ki_pid > p1->ki_pid); /* tie - return highest pid */
98	}
99	/*
100	 * pick the one with the smallest sleep time
101	 */
102	if (p2->ki_slptime > p1->ki_slptime)
103		return (0);
104	if (p1->ki_slptime > p2->ki_slptime)
105		return (1);
106	/*
107	 * favor one sleeping in a non-interruptible sleep
108	 */
109	if (p1->ki_tdflags & TDF_SINTR && (p2->ki_tdflags & TDF_SINTR) == 0)
110		return (1);
111	if (p2->ki_tdflags & TDF_SINTR && (p1->ki_tdflags & TDF_SINTR) == 0)
112		return (0);
113	return (p2->ki_pid > p1->ki_pid);	/* tie - return highest pid */
114}
115