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Gregory Haskins6e0534f2008-05-12 21:21:01 +02001/*
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 */
33static 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
Rusty Russell13b8bd02009-03-25 15:01:22 +103058 * @lowest_mask: A mask to fill in with selected CPUs (or NULL)
Gregory Haskins6e0534f2008-05-12 21:21:01 +020059 *
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 */
69int cpupri_find(struct cpupri *cp, struct task_struct *p,
Rusty Russell68e74562008-11-25 02:35:13 +103070 struct cpumask *lowest_mask)
Gregory Haskins6e0534f2008-05-12 21:21:01 +020071{
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];
Gregory Haskins6e0534f2008-05-12 21:21:01 +020077
78 if (idx >= task_pri)
79 break;
80
Rusty Russell68e74562008-11-25 02:35:13 +103081 if (cpumask_any_and(&p->cpus_allowed, vec->mask) >= nr_cpu_ids)
Gregory Haskins6e0534f2008-05-12 21:21:01 +020082 continue;
83
Gregory Haskins07903af2009-07-30 10:57:28 -040084 if (lowest_mask) {
Rusty Russell13b8bd02009-03-25 15:01:22 +103085 cpumask_and(lowest_mask, &p->cpus_allowed, vec->mask);
Gregory Haskins07903af2009-07-30 10:57:28 -040086
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
Gregory Haskins6e0534f2008-05-12 21:21:01 +020099 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 */
115void 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
Steven Rostedtc3a2ae32009-07-29 00:21:23 -0400130 * need to map it to the new value then remove the old value.
131 * Note, we must add the new value first, otherwise we risk the
132 * cpu being cleared from pri_active, and this cpu could be
133 * missed for a push or pull.
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200134 */
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200135 if (likely(newpri != CPUPRI_INVALID)) {
136 struct cpupri_vec *vec = &cp->pri_to_cpu[newpri];
137
138 spin_lock_irqsave(&vec->lock, flags);
139
Rusty Russell68e74562008-11-25 02:35:13 +1030140 cpumask_set_cpu(cpu, vec->mask);
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200141 vec->count++;
142 if (vec->count == 1)
143 set_bit(newpri, cp->pri_active);
144
145 spin_unlock_irqrestore(&vec->lock, flags);
146 }
Steven Rostedtc3a2ae32009-07-29 00:21:23 -0400147 if (likely(oldpri != CPUPRI_INVALID)) {
148 struct cpupri_vec *vec = &cp->pri_to_cpu[oldpri];
149
150 spin_lock_irqsave(&vec->lock, flags);
151
152 vec->count--;
153 if (!vec->count)
154 clear_bit(oldpri, cp->pri_active);
155 cpumask_clear_cpu(cpu, vec->mask);
156
157 spin_unlock_irqrestore(&vec->lock, flags);
158 }
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200159
160 *currpri = newpri;
161}
162
163/**
164 * cpupri_init - initialize the cpupri structure
165 * @cp: The cpupri context
Rusty Russell68e74562008-11-25 02:35:13 +1030166 * @bootmem: true if allocations need to use bootmem
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200167 *
Rusty Russell68e74562008-11-25 02:35:13 +1030168 * Returns: -ENOMEM if memory fails.
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200169 */
Li Zefanfd5e1b52009-06-15 13:34:19 +0800170int cpupri_init(struct cpupri *cp, bool bootmem)
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200171{
Pekka Enberg0fb53022009-06-11 08:41:22 +0300172 gfp_t gfp = GFP_KERNEL;
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200173 int i;
174
Pekka Enberg0fb53022009-06-11 08:41:22 +0300175 if (bootmem)
176 gfp = GFP_NOWAIT;
177
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200178 memset(cp, 0, sizeof(*cp));
179
180 for (i = 0; i < CPUPRI_NR_PRIORITIES; i++) {
181 struct cpupri_vec *vec = &cp->pri_to_cpu[i];
182
183 spin_lock_init(&vec->lock);
184 vec->count = 0;
Pekka Enberg0fb53022009-06-11 08:41:22 +0300185 if (!zalloc_cpumask_var(&vec->mask, gfp))
Rusty Russell68e74562008-11-25 02:35:13 +1030186 goto cleanup;
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200187 }
188
189 for_each_possible_cpu(i)
190 cp->cpu_to_pri[i] = CPUPRI_INVALID;
Rusty Russell68e74562008-11-25 02:35:13 +1030191 return 0;
192
193cleanup:
194 for (i--; i >= 0; i--)
195 free_cpumask_var(cp->pri_to_cpu[i].mask);
196 return -ENOMEM;
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200197}
198
Rusty Russell68e74562008-11-25 02:35:13 +1030199/**
200 * cpupri_cleanup - clean up the cpupri structure
201 * @cp: The cpupri context
202 */
203void cpupri_cleanup(struct cpupri *cp)
204{
205 int i;
Gregory Haskins6e0534f2008-05-12 21:21:01 +0200206
Rusty Russell68e74562008-11-25 02:35:13 +1030207 for (i = 0; i < CPUPRI_NR_PRIORITIES; i++)
208 free_cpumask_var(cp->pri_to_cpu[i].mask);
209}