xref: /openbmc/linux/arch/arm/kernel/topology.c (revision d23b3bf8)
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 rebalance_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  */
parse_dt_topology(void)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  */
update_cpu_capacity(unsigned int cpu)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
parse_dt_topology(void)176 static inline void parse_dt_topology(void) {}
update_cpu_capacity(unsigned int cpuid)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  */
store_cpu_topology(unsigned int cpuid)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  */
init_cpu_topology(void)239 void __init init_cpu_topology(void)
240 {
241 	reset_cpu_topology();
242 	smp_wmb();
243 
244 	parse_dt_topology();
245 }
246