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 */
convert_prio(int prio)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 */
cpupri_find(struct cpupri * cp,struct task_struct * p,struct cpumask * lowest_mask)69 int cpupri_find(struct cpupri *cp, struct task_struct *p,
70 struct cpumask *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
78 if (idx >= task_pri)
79 break;
80
81 if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
82 continue;
83
84 cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
85 return 1;
86 }
87
88 return 0;
89 }
90
91 /**
92 * cpupri_set - update the cpu priority setting
93 * @cp: The cpupri context
94 * @cpu: The target cpu
95 * @pri: The priority (INVALID-RT99) to assign to this CPU
96 *
97 * Note: Assumes cpu_rq(cpu)->lock is locked
98 *
99 * Returns: (void)
100 */
cpupri_set(struct cpupri * cp,int cpu,int newpri)101 void cpupri_set(struct cpupri *cp, int cpu, int newpri)
102 {
103 int *currpri = &cp->cpu_to_pri[cpu];
104 int oldpri = *currpri;
105 unsigned long flags;
106
107 newpri = convert_prio(newpri);
108
109 BUG_ON(newpri >= CPUPRI_NR_PRIORITIES);
110
111 if (newpri == oldpri)
112 return;
113
114 /*
115 * If the cpu was currently mapped to a different value, we
116 * first need to unmap the old value
117 */
118 if (likely(oldpri != CPUPRI_INVALID)) {
119 struct cpupri_vec *vec = &cp->pri_to_cpu[oldpri];
120
121 spin_lock_irqsave(&vec->lock, flags);
122
123 vec->count--;
124 if (!vec->count)
125 clear_bit(oldpri, cp->pri_active);
126 cpumask_clear_cpu(cpu, vec->mask);
127
128 spin_unlock_irqrestore(&vec->lock, flags);
129 }
130
131 if (likely(newpri != CPUPRI_INVALID)) {
132 struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
133
134 spin_lock_irqsave(&vec->lock, flags);
135
136 cpumask_set_cpu(cpu, vec->mask);
137 vec->count++;
138 if (vec->count == 1)
139 set_bit(newpri, cp->pri_active);
140
141 spin_unlock_irqrestore(&vec->lock, flags);
142 }
143
144 *currpri = newpri;
145 }
146
147 /**
148 * cpupri_init - initialize the cpupri structure
149 * @cp: The cpupri context
150 * @bootmem: true if allocations need to use bootmem
151 *
152 * Returns: -ENOMEM if memory fails.
153 */
cpupri_init(struct cpupri * cp,bool bootmem)154 int __init_refok cpupri_init(struct cpupri *cp, bool bootmem)
155 {
156 int i;
157
158 memset(cp, 0, sizeof(*cp));
159
160 for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
161 struct cpupri_vec *vec = &cp->pri_to_cpu[i];
162
163 spin_lock_init(&vec->lock);
164 vec->count = 0;
165 if (bootmem)
166 alloc_bootmem_cpumask_var(&vec->mask);
167 else if (!alloc_cpumask_var(&vec->mask, GFP_KERNEL))
168 goto cleanup;
169 }
170
171 for_each_possible_cpu(i)
172 cp->cpu_to_pri[i] = CPUPRI_INVALID;
173 return 0;
174
175 cleanup:
176 for (i--; i >= 0; i--)
177 free_cpumask_var(cp->pri_to_cpu[i].mask);
178 return -ENOMEM;
179 }
180
181 /**
182 * cpupri_cleanup - clean up the cpupri structure
183 * @cp: The cpupri context
184 */
cpupri_cleanup(struct cpupri * cp)185 void cpupri_cleanup(struct cpupri *cp)
186 {
187 int i;
188
189 for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
190 free_cpumask_var(cp->pri_to_cpu[i].mask);
191 }
192