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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 (or NULL) |
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 | 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 | if (lowest_mask) { |
85 | cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask); |
86 | |
87 | /* |
88 | * We have to ensure that we have at least one bit |
89 | * still set in the array, since the map could have |
90 | * been concurrently emptied between the first and |
91 | * second reads of vec->mask. If we hit this |
92 | * condition, simply act as though we never hit this |
93 | * priority level and continue on. |
94 | */ |
95 | if (cpumask_any(lowest_mask) >= nr_cpu_ids) |
96 | continue; |
97 | } |
98 | |
99 | return 1; |
100 | } |
101 | |
102 | return 0; |
103 | } |
104 | |
105 | /** |
106 | * cpupri_set - update the cpu priority setting |
107 | * @cp: The cpupri context |
108 | * @cpu: The target cpu |
109 | * @pri: The priority (INVALID-RT99) to assign to this CPU |
110 | * |
111 | * Note: Assumes cpu_rq(cpu)->lock is locked |
112 | * |
113 | * Returns: (void) |
114 | */ |
115 | void cpupri_set(struct cpupri *cp, int cpu, int newpri) |
116 | { |
117 | int *currpri = &cp->cpu_to_pri[cpu]; |
118 | int oldpri = *currpri; |
119 | unsigned long flags; |
120 | |
121 | newpri = convert_prio(newpri); |
122 | |
123 | BUG_ON(newpri >= CPUPRI_NR_PRIORITIES); |
124 | |
125 | if (newpri == oldpri) |
126 | return; |
127 | |
128 | /* |
129 | * If the cpu was currently mapped to a different value, we |
130 | * first need to unmap the old value |
131 | */ |
132 | if (likely(oldpri != CPUPRI_INVALID)) { |
133 | struct cpupri_vec *vec = &cp->pri_to_cpu[oldpri]; |
134 | |
135 | spin_lock_irqsave(&vec->lock, flags); |
136 | |
137 | vec->count--; |
138 | if (!vec->count) |
139 | clear_bit(oldpri, cp->pri_active); |
140 | cpumask_clear_cpu(cpu, vec->mask); |
141 | |
142 | spin_unlock_irqrestore(&vec->lock, flags); |
143 | } |
144 | |
145 | if (likely(newpri != CPUPRI_INVALID)) { |
146 | struct cpupri_vec *vec = &cp->pri_to_cpu[newpri]; |
147 | |
148 | spin_lock_irqsave(&vec->lock, flags); |
149 | |
150 | cpumask_set_cpu(cpu, vec->mask); |
151 | vec->count++; |
152 | if (vec->count == 1) |
153 | set_bit(newpri, cp->pri_active); |
154 | |
155 | spin_unlock_irqrestore(&vec->lock, flags); |
156 | } |
157 | |
158 | *currpri = newpri; |
159 | } |
160 | |
161 | /** |
162 | * cpupri_init - initialize the cpupri structure |
163 | * @cp: The cpupri context |
164 | * @bootmem: true if allocations need to use bootmem |
165 | * |
166 | * Returns: -ENOMEM if memory fails. |
167 | */ |
168 | int cpupri_init(struct cpupri *cp, bool bootmem) |
169 | { |
170 | gfp_t gfp = GFP_KERNEL; |
171 | int i; |
172 | |
173 | if (bootmem) |
174 | gfp = GFP_NOWAIT; |
175 | |
176 | memset(cp, 0, sizeof(*cp)); |
177 | |
178 | for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) { |
179 | struct cpupri_vec *vec = &cp->pri_to_cpu[i]; |
180 | |
181 | spin_lock_init(&vec->lock); |
182 | vec->count = 0; |
183 | if (!zalloc_cpumask_var(&vec->mask, gfp)) |
184 | goto cleanup; |
185 | } |
186 | |
187 | for_each_possible_cpu(i) |
188 | cp->cpu_to_pri[i] = CPUPRI_INVALID; |
189 | return 0; |
190 | |
191 | cleanup: |
192 | for (i--; i >= 0; i--) |
193 | free_cpumask_var(cp->pri_to_cpu[i].mask); |
194 | return -ENOMEM; |
195 | } |
196 | |
197 | /** |
198 | * cpupri_cleanup - clean up the cpupri structure |
199 | * @cp: The cpupri context |
200 | */ |
201 | void cpupri_cleanup(struct cpupri *cp) |
202 | { |
203 | int i; |
204 | |
205 | for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) |
206 | free_cpumask_var(cp->pri_to_cpu[i].mask); |
207 | } |
208 |
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