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 capacity scale management
  30  */
  31
  32 /*
  33  * cpu capacity 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_capacity field so the scheduler
  37  * can take this difference into account during load balance. A per cpu
  38  * structure is preferred because each CPU updates its own cpu_capacity field
  39  * during the load balance except for idle cores. One idle core is selected
  40  * to run the rebalance_domains for all idle cores and the cpu_capacity can be
  41  * updated during this sequence.
  42  */
  43 static DEFINE_PER_CPU(unsigned long, cpu_scale);
  44
  45 unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
  46 {
  47         return per_cpu(cpu_scale, cpu);
  48 }
  49
  50 static void set_capacity_scale(unsigned int cpu, unsigned long capacity)
  51 {
  52         per_cpu(cpu_scale, cpu) = capacity;
  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_CAPACITY_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_CAPACITY_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_capacity field such that an
  87  * 'average' CPU is of middle capacity. Also see the comments near
  88  * table_efficiency[] and update_cpu_capacity().
  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 = ULONG_MAX;
  95         unsigned long max_capacity = 0;
  96         unsigned long capacity = 0;
  97         int cpu = 0;
  98
  99         __cpu_capacity = kcalloc(nr_cpu_ids, sizeof(*__cpu_capacity),
 100                                  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_CAPACITY_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_CAPACITY_SHIFT+1);
 150         else
 151                 middle_capacity = ((max_capacity / 3)
 152                                 >> (SCHED_CAPACITY_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_capacity(unsigned int cpu)
 162 {
 163         if (!cpu_capacity(cpu))
 164                 return;
 165
 166         set_capacity_scale(cpu, cpu_capacity(cpu) / middle_capacity);
 167
 168         pr_info("CPU%u: update cpu_capacity %lu\n",
 169                 cpu, arch_scale_cpu_capacity(NULL, cpu));
 170 }
 171
 172 #else
 173 static inline void parse_dt_topology(void) {}
 174 static inline void update_cpu_capacity(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 /*
 189  * The current assumption is that we can power gate each core independently.
 190  * This will be superseded by DT binding once available.
 191  */
 192 const struct cpumask *cpu_corepower_mask(int cpu)
 193 {
 194         return &cpu_topology[cpu].thread_sibling;
 195 }
 196
 197 static void update_siblings_masks(unsigned int cpuid)
 198 {
 199         struct cputopo_arm *cpu_topo, *cpuid_topo = &cpu_topology[cpuid];
 200         int cpu;
 201
 202         /* update core and thread sibling masks */
 203         for_each_possible_cpu(cpu) {
 204                 cpu_topo = &cpu_topology[cpu];
 205
 206                 if (cpuid_topo->socket_id != cpu_topo->socket_id)
 207                         continue;
 208
 209                 cpumask_set_cpu(cpuid, &cpu_topo->core_sibling);
 210                 if (cpu != cpuid)
 211                         cpumask_set_cpu(cpu, &cpuid_topo->core_sibling);
 212
 213                 if (cpuid_topo->core_id != cpu_topo->core_id)
 214                         continue;
 215
 216                 cpumask_set_cpu(cpuid, &cpu_topo->thread_sibling);
 217                 if (cpu != cpuid)
 218                         cpumask_set_cpu(cpu, &cpuid_topo->thread_sibling);
 219         }
 220         smp_wmb();
 221 }
 222
 223 /*
 224  * store_cpu_topology is called at boot when only one cpu is running
 225  * and with the mutex cpu_hotplug.lock locked, when several cpus have booted,
 226  * which prevents simultaneous write access to cpu_topology array
 227  */
 228 void store_cpu_topology(unsigned int cpuid)
 229 {
 230         struct cputopo_arm *cpuid_topo = &cpu_topology[cpuid];
 231         unsigned int mpidr;
 232
 233         /* If the cpu topology has been already set, just return */
 234         if (cpuid_topo->core_id != -1)
 235                 return;
 236
 237         mpidr = read_cpuid_mpidr();
 238
 239         /* create cpu topology mapping */
 240         if ((mpidr & MPIDR_SMP_BITMASK) == MPIDR_SMP_VALUE) {
 241                 /*
 242                  * This is a multiprocessor system
 243                  * multiprocessor format & multiprocessor mode field are set
 244                  */
 245
 246                 if (mpidr & MPIDR_MT_BITMASK) {
 247                         /* core performance interdependency */
 248                         cpuid_topo->thread_id = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 249                         cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 250                         cpuid_topo->socket_id = MPIDR_AFFINITY_LEVEL(mpidr, 2);
 251                 } else {
 252                         /* largely independent cores */
 253                         cpuid_topo->thread_id = -1;
 254                         cpuid_topo->core_id = MPIDR_AFFINITY_LEVEL(mpidr, 0);
 255                         cpuid_topo->socket_id = MPIDR_AFFINITY_LEVEL(mpidr, 1);
 256                 }
 257         } else {
 258                 /*
 259                  * This is an uniprocessor system
 260                  * we are in multiprocessor format but uniprocessor system
 261                  * or in the old uniprocessor format
 262                  */
 263                 cpuid_topo->thread_id = -1;
 264                 cpuid_topo->core_id = 0;
 265                 cpuid_topo->socket_id = -1;
 266         }
 267
 268         update_siblings_masks(cpuid);
 269
 270         update_cpu_capacity(cpuid);
 271
 272         pr_info("CPU%u: thread %d, cpu %d, socket %d, mpidr %x\n",
 273                 cpuid, cpu_topology[cpuid].thread_id,
 274                 cpu_topology[cpuid].core_id,
 275                 cpu_topology[cpuid].socket_id, mpidr);
 276 }
 277
 278 static inline int cpu_corepower_flags(void)
 279 {
 280         return SD_SHARE_PKG_RESOURCES  | SD_SHARE_POWERDOMAIN;
 281 }
 282
 283 static struct sched_domain_topology_level arm_topology[] = {
 284 #ifdef CONFIG_SCHED_MC
 285         { cpu_corepower_mask, cpu_corepower_flags, SD_INIT_NAME(GMC) },
 286         { cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
 287 #endif
 288         { cpu_cpu_mask, SD_INIT_NAME(DIE) },
 289         { NULL, },
 290 };
 291
 292 /*
 293  * init_cpu_topology is called at boot when only one cpu is running
 294  * which prevent simultaneous write access to cpu_topology array
 295  */
 296 void __init init_cpu_topology(void)
 297 {
 298         unsigned int cpu;
 299
 300         /* init core mask and capacity */
 301         for_each_possible_cpu(cpu) {
 302                 struct cputopo_arm *cpu_topo = &(cpu_topology[cpu]);
 303
 304                 cpu_topo->thread_id = -1;
 305                 cpu_topo->core_id =  -1;
 306                 cpu_topo->socket_id = -1;
 307                 cpumask_clear(&cpu_topo->core_sibling);
 308                 cpumask_clear(&cpu_topo->thread_sibling);
 309
 310                 set_capacity_scale(cpu, SCHED_CAPACITY_SCALE);
 311         }
 312         smp_wmb();
 313
 314         parse_dt_topology();
 315
 316         /* Set scheduler topology descriptor */
 317         set_sched_topology(arm_topology);
 318 }