1 /*
2 * kernel/sched_cpupri.c
3 *
4 * CPU priority management
5 *
6 * Copyright (C) 2007-2008 Novell
7 *
8 * Author: Gregory Haskins <ghaskins@novell.com>
9 *
10 * This code tracks the priority of each CPU so that global migration
11 * decisions are easy to calculate. Each CPU can be in a state as follows:
12 *
13 * (INVALID), IDLE, NORMAL, RT1, ... RT99
14 *
15 * going from the lowest priority to the highest. CPUs in the INVALID state
16 * are not eligible for routing. The system maintains this state with
17 * a 2 dimensional bitmap (the first for priority class, the second for cpus
18 * in that class). Therefore a typical application without affinity
19 * restrictions can find a suitable CPU with O(1) complexity (e.g. two bit
20 * searches). For tasks with affinity restrictions, the algorithm has a
21 * worst case complexity of O(min(102, nr_domcpus)), though the scenario that
22 * yields the worst case search is fairly contrived.
23 *
24 * This program is free software; you can redistribute it and/or
25 * modify it under the terms of the GNU General Public License
26 * as published by the Free Software Foundation; version 2
27 * of the License.
28 */
29
30 #include "sched_cpupri.h"
31
32 /* Convert between a 140 based task->prio, and our 102 based cpupri */
33 static int convert_prio(int prio)
34 {
35 int cpupri;
36
37 if (prio == CPUPRI_INVALID)
38 cpupri = CPUPRI_INVALID;
39 else if (prio == MAX_PRIO)
40 cpupri = CPUPRI_IDLE;
41 else if (prio >= MAX_RT_PRIO)
42 cpupri = CPUPRI_NORMAL;
43 else
44 cpupri = MAX_RT_PRIO - prio + 1;
45
46 return cpupri;
47 }
48
49 #define for_each_cpupri_active(array, idx) \
50 for (idx = find_first_bit(array, CPUPRI_NR_PRIORITIES); \
51 idx < CPUPRI_NR_PRIORITIES; \
52 idx = find_next_bit(array, CPUPRI_NR_PRIORITIES, idx+1))
53
54 /**
55 * cpupri_find - find the best (lowest-pri) CPU in the system
56 * @cp: The cpupri context
57 * @p: The task
58 * @lowest_mask: A mask to fill in with selected CPUs
59 *
60 * Note: This function returns the recommended CPUs as calculated during the
61 * current invokation. By the time the call returns, the CPUs may have in
62 * fact changed priorities any number of times. While not ideal, it is not
63 * an issue of correctness since the normal rebalancer logic will correct
64 * any discrepancies created by racing against the uncertainty of the current
65 * priority configuration.
66 *
67 * Returns: (int)bool - CPUs were found
68 */
69 int cpupri_find(struct cpupri *cp, struct task_struct *p,
70 cpumask_t *lowest_mask)
71 {
72 int idx = 0;
73 int task_pri = convert_prio(p->prio);
74
75 for_each_cpupri_active(cp->pri_active, idx) {
76 struct cpupri_vec *vec = &cp->pri_to_cpu[idx];
77 cpumask_t mask;
78
79 if (idx >= task_pri)
80 break;
81
82 cpus_and(mask, p->cpus_allowed, vec->mask);
83
84 if (cpus_empty(mask))
85 continue;
86
87 *lowest_mask = mask;
88 return 1;
89 }
90
91 return 0;
92 }
93
94 /**
95 * cpupri_set - update the cpu priority setting
96 * @cp: The cpupri context
97 * @cpu: The target cpu
98 * @pri: The priority (INVALID-RT99) to assign to this CPU
99 *
100 * Note: Assumes cpu_rq(cpu)->lock is locked
101 *
102 * Returns: (void)
103 */
104 void cpupri_set(struct cpupri *cp, int cpu, int newpri)
105 {
106 int *currpri = &cp->cpu_to_pri[cpu];
107 int oldpri = *currpri;
108 unsigned long flags;
109
110 newpri = convert_prio(newpri);
111
112 BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
113
114 if (newpri == oldpri)
115 return;
116
117 /*
118 * If the cpu was currently mapped to a different value, we
119 * first need to unmap the old value
120 */
121 if (likely(oldpri != CPUPRI_INVALID)) {
122 struct cpupri_vec *vec = &cp->pri_to_cpu[oldpri];
123
124 spin_lock_irqsave(&vec->lock, flags);
125
126 vec->count--;
127 if (!vec->count)
128 clear_bit(oldpri, cp->pri_active);
129 cpu_clear(cpu, vec->mask);
130
131 spin_unlock_irqrestore(&vec->lock, flags);
132 }
133
134 if (likely(newpri != CPUPRI_INVALID)) {
135 struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
136
137 spin_lock_irqsave(&vec->lock, flags);
138
139 cpu_set(cpu, vec->mask);
140 vec->count++;
141 if (vec->count == 1)
142 set_bit(newpri, cp->pri_active);
143
144 spin_unlock_irqrestore(&vec->lock, flags);
145 }
146
147 *currpri = newpri;
148 }
149
150 /**
151 * cpupri_init - initialize the cpupri structure
152 * @cp: The cpupri context
153 *
154 * Returns: (void)
155 */
156 void cpupri_init(struct cpupri *cp)
157 {
158 int i;
159
160 memset(cp, 0, sizeof(*cp));
161
162 for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
163 struct cpupri_vec *vec = &cp->pri_to_cpu[i];
164
165 spin_lock_init(&vec->lock);
166 vec->count = 0;
167 cpus_clear(vec->mask);
168 }
169
170 for_each_possible_cpu(i)
171 cp->cpu_to_pri[i] = CPUPRI_INVALID;
172 }
173
174
175
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