arch/arm/kernel/topology.c

   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/cpu.h>
  15 #include <linux/cpumask.h>
  16 #include <linux/export.h>
  17 #include <linux/init.h>
  18 #include <linux/percpu.h>
  19 #include <linux/node.h>
  20 #include <linux/nodemask.h>
  21 #include <linux/of.h>
  22 #include <linux/sched.h>
  23 #include <linux/slab.h>
  24
  25 #include <asm/cputype.h>
  26 #include <asm/topology.h>
  27
  28 /*
  29  * cpu power scale management
  30  */
  31
  32 /*
  33  * cpu power table
  34  * This per cpu data structure describes the relative capacity of each core.
  35  * On a heteregenous system, cores don't have the same computation capacity
  36  * and we reflect that difference in the cpu_power field so the scheduler can
  37  * take this difference into account during load balance. A per cpu structure
  38  * is preferred because each CPU updates its own cpu_power field during the
  39  * load balance except for idle cores. One idle core is selected to run the
  40  * rebalance_domains for all idle cores and the cpu_power can be updated
  41  * during this sequence.
  42  */
  43 static DEFINE_PER_CPU(unsigned long, cpu_scale);
  44
  45 unsigned long arch_scale_freq_power(struct sched_domain *sd, int cpu)
  46 {
  47         return per_cpu(cpu_scale, cpu);
  48 }
  49
  50 static void set_power_scale(unsigned int cpu, unsigned long power)
  51 {
  52         per_cpu(cpu_scale, cpu) = power;
  53 }
  54
  55 #ifdef CONFIG_OF
  56 struct cpu_efficiency {
  57         const char *compatible;
  58         unsigned long efficiency;
  59 };
  60
  61 /*
  62  * Table of relative efficiency of each processors
  63  * The efficiency value must fit in 20bit and the final
  64  * cpu_scale value must be in the range
  65  *   0 < cpu_scale < 3*SCHED_POWER_SCALE/2
  66  * in order to return at most 1 when DIV_ROUND_CLOSEST
  67  * is used to compute the capacity of a CPU.
  68  * Processors that are not defined in the table,
  69  * use the default SCHED_POWER_SCALE value for cpu_scale.
  70  */
  71 static const struct cpu_efficiency table_efficiency[] = {
  72         {"arm,cortex-a15", 3891},
  73         {"arm,cortex-a7",  2048},
  74         {NULL, },
  75 };
  76
  77 static unsigned long *__cpu_capacity;
  78 #define cpu_capacity(cpu)       __cpu_capacity[cpu]
  79
  80 static unsigned long middle_capacity = 1;
  81
  82 /*
  83  * Iterate all CPUs' descriptor in DT and compute the efficiency
  84  * (as per table_efficiency). Also calculate a middle efficiency
  85  * as close as possible to  (max{eff_i} - min{eff_i}) / 2
  86  * This is later used to scale the cpu_power field such that an
  87  * 'average' CPU is of middle power. Also see the comments near
  88  * table_efficiency[] and update_cpu_power().
  89  */
  90 static void __init parse_dt_topology(void)
  91 {
  92         const struct cpu_efficiency *cpu_eff;
  93         struct device_node *cn = NULL;
  94         unsigned long min_capacity = (unsigned long)(-1);
  95         unsigned long max_capacity = 0;
  96         unsigned long capacity = 0;
  97         int alloc_size, cpu = 0;
  98
  99         alloc_size = nr_cpu_ids * sizeof(*__cpu_capacity);
 100         __cpu_capacity = kzalloc(alloc_size, GFP_NOWAIT);
 101
 102         for_each_possible_cpu(cpu) {
 103                 const u32 *rate;
 104                 int len;
 105
 106                 /* too early to use cpu->of_node */
 107                 cn = of_get_cpu_node(cpu, NULL);
 108                 if (!cn) {
 109                         pr_err("missing device node for CPU %d\n", cpu);
 110                         continue;
 111                 }
 112
 113                 for (cpu_eff = table_efficiency; cpu_eff->compatible; cpu_eff++)
 114                         if (of_device_is_compatible(cn, cpu_eff->compatible))
 115                                 break;
 116
 117                 if (cpu_eff->compatible == NULL)
 118                         continue;
 119
 120                 rate = of_get_property(cn, "clock-frequency", &len);
 121                 if (!rate || len != 4) {
 122                         pr_err("%s missing clock-frequency property\n",
 123                                 cn->full_name);
 124                         continue;
 125                 }
 126
 127                 capacity = ((be32_to_cpup(rate)) >> 20) * cpu_eff->efficiency;
 128
 129                 /* Save min capacity of the system */
 130                 if (capacity < min_capacity)
 131                         min_capacity = capacity;
 132
 133                 /* Save max capacity of the system */
 134                 if (capacity > max_capacity)
 135                         max_capacity = capacity;
 136
 137                 cpu_capacity(cpu) = capacity;
 138         }
 139
 140         /* If min and max capacities are equals, we bypass the update of the
 141          * cpu_scale because all CPUs have the same capacity. Otherwise, we
 142          * compute a middle_capacity factor that will ensure that the capacity
 143          * of an 'average' CPU of the system will be as close as possible to
 144          * SCHED_POWER_SCALE, which is the default value, but with the
 145          * constraint explained near table_efficiency[].
 146          */
 147         if (4*max_capacity < (3*(max_capacity + min_capacity)))
 148                 middle_capacity = (min_capacity + max_capacity)
 149                                 >> (SCHED_POWER_SHIFT+1);
 150         else
 151                 middle_capacity = ((max_capacity / 3)
 152                                 >> (SCHED_POWER_SHIFT-1)) + 1;
 153
 154 }
 155
 156 /*
 157  * Look for a customed capacity of a CPU in the cpu_capacity table during the
 158  * boot. The update of all CPUs is in O(n^2) for heteregeneous system but the
 159  * function returns directly for SMP system.
 160  */
 161 static void update_cpu_power(unsigned int cpu)
 162 {
 163         if (!cpu_capacity(cpu))
 164                 return;
 165
 166         set_power_scale(cpu, cpu_capacity(cpu) / middle_capacity);
 167
 168         printk(KERN_INFO "CPU%u: update cpu_power %lu\n",
 169                 cpu, arch_scale_freq_power(NULL, cpu));
 170 }
 171
 172 #else
 173 static inline void parse_dt_topology(void) {}
 174 static inline void update_cpu_power(unsigned int cpuid) {}
 175 #endif
 176
 177  /*
 178  * cpu topology table
 179  */
 180 struct cputopo_arm cpu_topology[NR_CPUS];
 181 EXPORT_SYMBOL_GPL(cpu_topology);
 182
 183 const struct cpumask *cpu_coregroup_mask(int cpu)
 184 {
 185         return &cpu_topology[cpu].core_sibling;
 186 }
 187
 188 static void update_siblings_masks(unsigned int cpuid)
 189 {
 190         struct cputopo_arm *cpu_topo, *cpuid_topo = &cpu_topology[cpuid];
 191         int cpu;
 192
 193         /* update core and thread sibling masks */
 194         for_each_possible_cpu(cpu) {
 195                 cpu_topo = &cpu_topology[cpu];
 196
 197                 if (cpuid_topo->socket_id != cpu_topo->socket_id)
 198                         continue;
 199
 200                 cpumask_set_cpu(cpuid, &cpu_topo->core_sibling);
 201                 if (cpu != cpuid)
 202                         cpumask_set_cpu(cpu, &cpuid_topo->core_sibling);
 203
 204                 if (cpuid_topo->core_id != cpu_topo->core_id)
 205                         continue;
 206
 207                 cpumask_set_cpu(cpuid, &cpu_topo->thread_sibling);
 208                 if (cpu != cpuid)
 209                         cpumask_set_cpu(cpu, &cpuid_topo->thread_sibling);
 210         }
 211         smp_wmb();
 212 }
 213
 214 /*
 215  * store_cpu_topology is called at boot when only one cpu is running
 216  * and with the mutex cpu_hotplug.lock locked, when several cpus have booted,
 217  * which prevents simultaneous write access to cpu_topology array
 218  */
 219 void store_cpu_topology(unsigned int cpuid)
 220 {
 221         struct cputopo_arm *cpuid_topo = &cpu_topology[cpuid];
 222         unsigned int mpidr;
 223
 224         /* If the cpu topology has been already set, just return */
 225         if (cpuid_topo->core_id != -1)
 226                 return;
 227
 228         mpidr = read_cpuid_mpidr();
 229
 230         /* create cpu topology mapping */
 231         if ((mpidr & MPIDR_SMP_BITMASK) == MPIDR_SMP_VALUE) {
 232                 /*
 233                  * This is a multiprocessor system
 234                  * multiprocessor format & multiprocessor mode field are set
 235                  */
 236
 237                 if (mpidr & MPIDR_MT_BITMASK) {
 238                         /* core performance interdependency */
 239                         cpuid_topo->thread_id = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 240                         cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 241                         cpuid_topo->socket_id = MPIDR_AFFINITY_LEVEL(mpidr, 2);
 242                 } else {
 243                         /* largely independent cores */
 244                         cpuid_topo->thread_id = -1;
 245                         cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 246                         cpuid_topo->socket_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 247                 }
 248         } else {
 249                 /*
 250                  * This is an uniprocessor system
 251                  * we are in multiprocessor format but uniprocessor system
 252                  * or in the old uniprocessor format
 253                  */
 254                 cpuid_topo->thread_id = -1;
 255                 cpuid_topo->core_id = 0;
 256                 cpuid_topo->socket_id = -1;
 257         }
 258
 259         update_siblings_masks(cpuid);
 260
 261         update_cpu_power(cpuid);
 262
 263         printk(KERN_INFO "CPU%u: thread %d, cpu %d, socket %d, mpidr %x\n",
 264                 cpuid, cpu_topology[cpuid].thread_id,
 265                 cpu_topology[cpuid].core_id,
 266                 cpu_topology[cpuid].socket_id, mpidr);
 267 }
 268
 269 /*
 270  * init_cpu_topology is called at boot when only one cpu is running
 271  * which prevent simultaneous write access to cpu_topology array
 272  */
 273 void __init init_cpu_topology(void)
 274 {
 275         unsigned int cpu;
 276
 277         /* init core mask and power*/
 278         for_each_possible_cpu(cpu) {
 279                 struct cputopo_arm *cpu_topo = &(cpu_topology[cpu]);
 280
 281                 cpu_topo->thread_id = -1;
 282                 cpu_topo->core_id =  -1;
 283                 cpu_topo->socket_id = -1;
 284                 cpumask_clear(&cpu_topo->core_sibling);
 285                 cpumask_clear(&cpu_topo->thread_sibling);
 286
 287                 set_power_scale(cpu, SCHED_POWER_SCALE);
 288         }
 289         smp_wmb();
 290
 291         parse_dt_topology();
 292 }