1 /*
2 * arch/arm/kernel/topology.c
3 *
4 * Copyright (C) 2011 Linaro Limited.
5 * Written by: Vincent Guittot
6 *
7 * based on arch/sh/kernel/topology.c
8 *
9 * This file is subject to the terms and conditions of the GNU General Public
10 * License. See the file "COPYING" in the main directory of this archive
11 * for more details.
12 */
13
14 #include <linux/arch_topology.h>
15 #include <linux/cpu.h>
16 #include <linux/cpufreq.h>
17 #include <linux/cpumask.h>
18 #include <linux/export.h>
19 #include <linux/init.h>
20 #include <linux/percpu.h>
21 #include <linux/node.h>
22 #include <linux/nodemask.h>
23 #include <linux/of.h>
24 #include <linux/sched.h>
25 #include <linux/sched/topology.h>
26 #include <linux/slab.h>
27 #include <linux/string.h>
28
29 #include <asm/cpu.h>
30 #include <asm/cputype.h>
31 #include <asm/topology.h>
32
33 /*
34 * cpu capacity scale management
35 */
36
37 /*
38 * cpu capacity table
39 * This per cpu data structure describes the relative capacity of each core.
40 * On a heteregenous system, cores don't have the same computation capacity
41 * and we reflect that difference in the cpu_capacity field so the scheduler
42 * can take this difference into account during load balance. A per cpu
43 * structure is preferred because each CPU updates its own cpu_capacity field
44 * during the load balance except for idle cores. One idle core is selected
45 * to run the sched_balance_domains for all idle cores and the cpu_capacity can be
46 * updated during this sequence.
47 */
48
49 #ifdef CONFIG_OF
50 struct cpu_efficiency {
51 const char *compatible;
52 unsigned long efficiency;
53 };
54
55 /*
56 * Table of relative efficiency of each processors
57 * The efficiency value must fit in 20bit and the final
58 * cpu_scale value must be in the range
59 * 0 < cpu_scale < 3*SCHED_CAPACITY_SCALE/2
60 * in order to return at most 1 when DIV_ROUND_CLOSEST
61 * is used to compute the capacity of a CPU.
62 * Processors that are not defined in the table,
63 * use the default SCHED_CAPACITY_SCALE value for cpu_scale.
64 */
65 static const struct cpu_efficiency table_efficiency[] = {
66 {"arm,cortex-a15", 3891},
67 {"arm,cortex-a7", 2048},
68 {NULL, },
69 };
70
71 static unsigned long *__cpu_capacity;
72 #define cpu_capacity(cpu) __cpu_capacity[cpu]
73
74 static unsigned long middle_capacity = 1;
75 static bool cap_from_dt = true;
76
77 /*
78 * Iterate all CPUs' descriptor in DT and compute the efficiency
79 * (as per table_efficiency). Also calculate a middle efficiency
80 * as close as possible to (max{eff_i} - min{eff_i}) / 2
81 * This is later used to scale the cpu_capacity field such that an
82 * 'average' CPU is of middle capacity. Also see the comments near
83 * table_efficiency[] and update_cpu_capacity().
84 */
85 static void __init parse_dt_topology(void)
86 {
87 const struct cpu_efficiency *cpu_eff;
88 struct device_node *cn = NULL;
89 unsigned long min_capacity = ULONG_MAX;
90 unsigned long max_capacity = 0;
91 unsigned long capacity = 0;
92 int cpu = 0;
93
94 __cpu_capacity = kcalloc(nr_cpu_ids, sizeof(*__cpu_capacity),
95 GFP_NOWAIT);
96
97 for_each_possible_cpu(cpu) {
98 const __be32 *rate;
99 int len;
100
101 /* too early to use cpu->of_node */
102 cn = of_get_cpu_node(cpu, NULL);
103 if (!cn) {
104 pr_err("missing device node for CPU %d\n", cpu);
105 continue;
106 }
107
108 if (topology_parse_cpu_capacity(cn, cpu)) {
109 of_node_put(cn);
110 continue;
111 }
112
113 cap_from_dt = false;
114
115 for (cpu_eff = table_efficiency; cpu_eff->compatible; cpu_eff++)
116 if (of_device_is_compatible(cn, cpu_eff->compatible))
117 break;
118
119 if (cpu_eff->compatible == NULL)
120 continue;
121
122 rate = of_get_property(cn, "clock-frequency", &len);
123 if (!rate || len != 4) {
124 pr_err("%pOF missing clock-frequency property\n", cn);
125 continue;
126 }
127
128 capacity = ((be32_to_cpup(rate)) >> 20) * cpu_eff->efficiency;
129
130 /* Save min capacity of the system */
131 if (capacity < min_capacity)
132 min_capacity = capacity;
133
134 /* Save max capacity of the system */
135 if (capacity > max_capacity)
136 max_capacity = capacity;
137
138 cpu_capacity(cpu) = capacity;
139 }
140
141 /* If min and max capacities are equals, we bypass the update of the
142 * cpu_scale because all CPUs have the same capacity. Otherwise, we
143 * compute a middle_capacity factor that will ensure that the capacity
144 * of an 'average' CPU of the system will be as close as possible to
145 * SCHED_CAPACITY_SCALE, which is the default value, but with the
146 * constraint explained near table_efficiency[].
147 */
148 if (4*max_capacity < (3*(max_capacity + min_capacity)))
149 middle_capacity = (min_capacity + max_capacity)
150 >> (SCHED_CAPACITY_SHIFT+1);
151 else
152 middle_capacity = ((max_capacity / 3)
153 >> (SCHED_CAPACITY_SHIFT-1)) + 1;
154
155 if (cap_from_dt)
156 topology_normalize_cpu_scale();
157 }
158
159 /*
160 * Look for a customed capacity of a CPU in the cpu_capacity table during the
161 * boot. The update of all CPUs is in O(n^2) for heteregeneous system but the
162 * function returns directly for SMP system.
163 */
164 static void update_cpu_capacity(unsigned int cpu)
165 {
166 if (!cpu_capacity(cpu) || cap_from_dt)
167 return;
168
169 topology_set_cpu_scale(cpu, cpu_capacity(cpu) / middle_capacity);
170
171 pr_info("CPU%u: update cpu_capacity %lu\n",
172 cpu, topology_get_cpu_scale(cpu));
173 }
174
175 #else
176 static inline void parse_dt_topology(void) {}
177 static inline void update_cpu_capacity(unsigned int cpuid) {}
178 #endif
179
180 /*
181 * store_cpu_topology is called at boot when only one cpu is running
182 * and with the mutex cpu_hotplug.lock locked, when several cpus have booted,
183 * which prevents simultaneous write access to cpu_topology array
184 */
185 void store_cpu_topology(unsigned int cpuid)
186 {
187 struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
188 unsigned int mpidr;
189
190 if (cpuid_topo->package_id != -1)
191 goto topology_populated;
192
193 mpidr = read_cpuid_mpidr();
194
195 /* create cpu topology mapping */
196 if ((mpidr & MPIDR_SMP_BITMASK) == MPIDR_SMP_VALUE) {
197 /*
198 * This is a multiprocessor system
199 * multiprocessor format & multiprocessor mode field are set
200 */
201
202 if (mpidr & MPIDR_MT_BITMASK) {
203 /* core performance interdependency */
204 cpuid_topo->thread_id = MPIDR_AFFINITY_LEVEL(mpidr, 0);
205 cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
206 cpuid_topo->package_id = MPIDR_AFFINITY_LEVEL(mpidr, 2);
207 } else {
208 /* largely independent cores */
209 cpuid_topo->thread_id = -1;
210 cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 0);
211 cpuid_topo->package_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
212 }
213 } else {
214 /*
215 * This is an uniprocessor system
216 * we are in multiprocessor format but uniprocessor system
217 * or in the old uniprocessor format
218 */
219 cpuid_topo->thread_id = -1;
220 cpuid_topo->core_id = 0;
221 cpuid_topo->package_id = -1;
222 }
223
224 update_cpu_capacity(cpuid);
225
226 pr_info("CPU%u: thread %d, cpu %d, socket %d, mpidr %x\n",
227 cpuid, cpu_topology[cpuid].thread_id,
228 cpu_topology[cpuid].core_id,
229 cpu_topology[cpuid].package_id, mpidr);
230
231 topology_populated:
232 update_siblings_masks(cpuid);
233 }
234
235 /*
236 * init_cpu_topology is called at boot when only one cpu is running
237 * which prevent simultaneous write access to cpu_topology array
238 */
239 void __init init_cpu_topology(void)
240 {
241 reset_cpu_topology();
242 smp_wmb();
243
244 parse_dt_topology();
245 }
246
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