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/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  */
  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 }