lib/cpu_rmap.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * cpu_rmap.c: CPU affinity reverse-map support
   4  * Copyright 2011 Solarflare Communications Inc.
   5  */
   6
   7 #include <linux/cpu_rmap.h>
   8 #include <linux/interrupt.h>
   9 #include <linux/export.h>
  10
  11 /*
  12  * These functions maintain a mapping from CPUs to some ordered set of
  13  * objects with CPU affinities.  This can be seen as a reverse-map of
  14  * CPU affinity.  However, we do not assume that the object affinities
  15  * cover all CPUs in the system.  For those CPUs not directly covered
  16  * by object affinities, we attempt to find a nearest object based on
  17  * CPU topology.
  18  */
  19
  20 /**
  21  * alloc_cpu_rmap - allocate CPU affinity reverse-map
  22  * @size: Number of objects to be mapped
  23  * @flags: Allocation flags e.g. %GFP_KERNEL
  24  */
  25 struct cpu_rmap *alloc_cpu_rmap(unsigned int size, gfp_t flags)
  26 {
  27         struct cpu_rmap *rmap;
  28         unsigned int cpu;
  29         size_t obj_offset;
  30
  31         /* This is a silly number of objects, and we use u16 indices. */
  32         if (size > 0xffff)
  33                 return NULL;
  34
  35         /* Offset of object pointer array from base structure */
  36         obj_offset = ALIGN(offsetof(struct cpu_rmap, near[nr_cpu_ids]),
  37                            sizeof(void *));
  38
  39         rmap = kzalloc(obj_offset + size * sizeof(rmap->obj[0]), flags);
  40         if (!rmap)
  41                 return NULL;
  42
  43         kref_init(&rmap->refcount);
  44         rmap->obj = (void **)((char *)rmap + obj_offset);
  45
  46         /* Initially assign CPUs to objects on a rota, since we have
  47          * no idea where the objects are.  Use infinite distance, so
  48          * any object with known distance is preferable.  Include the
  49          * CPUs that are not present/online, since we definitely want
  50          * any newly-hotplugged CPUs to have some object assigned.
  51          */
  52         for_each_possible_cpu(cpu) {
  53                 rmap->near[cpu].index = cpu % size;
  54                 rmap->near[cpu].dist = CPU_RMAP_DIST_INF;
  55         }
  56
  57         rmap->size = size;
  58         return rmap;
  59 }
  60 EXPORT_SYMBOL(alloc_cpu_rmap);
  61
  62 /**
  63  * cpu_rmap_release - internal reclaiming helper called from kref_put
  64  * @ref: kref to struct cpu_rmap
  65  */
  66 static void cpu_rmap_release(struct kref *ref)
  67 {
  68         struct cpu_rmap *rmap = container_of(ref, struct cpu_rmap, refcount);
  69         kfree(rmap);
  70 }
  71
  72 /**
  73  * cpu_rmap_get - internal helper to get new ref on a cpu_rmap
  74  * @rmap: reverse-map allocated with alloc_cpu_rmap()
  75  */
  76 static inline void cpu_rmap_get(struct cpu_rmap *rmap)
  77 {
  78         kref_get(&rmap->refcount);
  79 }
  80
  81 /**
  82  * cpu_rmap_put - release ref on a cpu_rmap
  83  * @rmap: reverse-map allocated with alloc_cpu_rmap()
  84  */
  85 int cpu_rmap_put(struct cpu_rmap *rmap)
  86 {
  87         return kref_put(&rmap->refcount, cpu_rmap_release);
  88 }
  89 EXPORT_SYMBOL(cpu_rmap_put);
  90
  91 /* Reevaluate nearest object for given CPU, comparing with the given
  92  * neighbours at the given distance.
  93  */
  94 static bool cpu_rmap_copy_neigh(struct cpu_rmap *rmap, unsigned int cpu,
  95                                 const struct cpumask *mask, u16 dist)
  96 {
  97         int neigh;
  98
  99         for_each_cpu(neigh, mask) {
 100                 if (rmap->near[cpu].dist > dist &&
 101                     rmap->near[neigh].dist <= dist) {
 102                         rmap->near[cpu].index = rmap->near[neigh].index;
 103                         rmap->near[cpu].dist = dist;
 104                         return true;
 105                 }
 106         }
 107         return false;
 108 }
 109
 110 #ifdef DEBUG
 111 static void debug_print_rmap(const struct cpu_rmap *rmap, const char *prefix)
 112 {
 113         unsigned index;
 114         unsigned int cpu;
 115
 116         pr_info("cpu_rmap %p, %s:\n", rmap, prefix);
 117
 118         for_each_possible_cpu(cpu) {
 119                 index = rmap->near[cpu].index;
 120                 pr_info("cpu %d -> obj %u (distance %u)\n",
 121                         cpu, index, rmap->near[cpu].dist);
 122         }
 123 }
 124 #else
 125 static inline void
 126 debug_print_rmap(const struct cpu_rmap *rmap, const char *prefix)
 127 {
 128 }
 129 #endif
 130
 131 /**
 132  * cpu_rmap_add - add object to a rmap
 133  * @rmap: CPU rmap allocated with alloc_cpu_rmap()
 134  * @obj: Object to add to rmap
 135  *
 136  * Return index of object.
 137  */
 138 int cpu_rmap_add(struct cpu_rmap *rmap, void *obj)
 139 {
 140         u16 index;
 141
 142         BUG_ON(rmap->used >= rmap->size);
 143         index = rmap->used++;
 144         rmap->obj[index] = obj;
 145         return index;
 146 }
 147 EXPORT_SYMBOL(cpu_rmap_add);
 148
 149 /**
 150  * cpu_rmap_update - update CPU rmap following a change of object affinity
 151  * @rmap: CPU rmap to update
 152  * @index: Index of object whose affinity changed
 153  * @affinity: New CPU affinity of object
 154  */
 155 int cpu_rmap_update(struct cpu_rmap *rmap, u16 index,
 156                     const struct cpumask *affinity)
 157 {
 158         cpumask_var_t update_mask;
 159         unsigned int cpu;
 160
 161         if (unlikely(!zalloc_cpumask_var(&update_mask, GFP_KERNEL)))
 162                 return -ENOMEM;
 163
 164         /* Invalidate distance for all CPUs for which this used to be
 165          * the nearest object.  Mark those CPUs for update.
 166          */
 167         for_each_online_cpu(cpu) {
 168                 if (rmap->near[cpu].index == index) {
 169                         rmap->near[cpu].dist = CPU_RMAP_DIST_INF;
 170                         cpumask_set_cpu(cpu, update_mask);
 171                 }
 172         }
 173
 174         debug_print_rmap(rmap, "after invalidating old distances");
 175
 176         /* Set distance to 0 for all CPUs in the new affinity mask.
 177          * Mark all CPUs within their NUMA nodes for update.
 178          */
 179         for_each_cpu(cpu, affinity) {
 180                 rmap->near[cpu].index = index;
 181                 rmap->near[cpu].dist = 0;
 182                 cpumask_or(update_mask, update_mask,
 183                            cpumask_of_node(cpu_to_node(cpu)));
 184         }
 185
 186         debug_print_rmap(rmap, "after updating neighbours");
 187
 188         /* Update distances based on topology */
 189         for_each_cpu(cpu, update_mask) {
 190                 if (cpu_rmap_copy_neigh(rmap, cpu,
 191                                         topology_sibling_cpumask(cpu), 1))
 192                         continue;
 193                 if (cpu_rmap_copy_neigh(rmap, cpu,
 194                                         topology_core_cpumask(cpu), 2))
 195                         continue;
 196                 if (cpu_rmap_copy_neigh(rmap, cpu,
 197                                         cpumask_of_node(cpu_to_node(cpu)), 3))
 198                         continue;
 199                 /* We could continue into NUMA node distances, but for now
 200                  * we give up.
 201                  */
 202         }
 203
 204         debug_print_rmap(rmap, "after copying neighbours");
 205
 206         free_cpumask_var(update_mask);
 207         return 0;
 208 }
 209 EXPORT_SYMBOL(cpu_rmap_update);
 210
 211 /* Glue between IRQ affinity notifiers and CPU rmaps */
 212
 213 struct irq_glue {
 214         struct irq_affinity_notify notify;
 215         struct cpu_rmap *rmap;
 216         u16 index;
 217 };
 218
 219 /**
 220  * free_irq_cpu_rmap - free a CPU affinity reverse-map used for IRQs
 221  * @rmap: Reverse-map allocated with alloc_irq_cpu_map(), or %NULL
 222  *
 223  * Must be called in process context, before freeing the IRQs.
 224  */
 225 void free_irq_cpu_rmap(struct cpu_rmap *rmap)
 226 {
 227         struct irq_glue *glue;
 228         u16 index;
 229
 230         if (!rmap)
 231                 return;
 232
 233         for (index = 0; index < rmap->used; index++) {
 234                 glue = rmap->obj[index];
 235                 irq_set_affinity_notifier(glue->notify.irq, NULL);
 236         }
 237
 238         cpu_rmap_put(rmap);
 239 }
 240 EXPORT_SYMBOL(free_irq_cpu_rmap);
 241
 242 /**
 243  * irq_cpu_rmap_notify - callback for IRQ subsystem when IRQ affinity updated
 244  * @notify: struct irq_affinity_notify passed by irq/manage.c
 245  * @mask: cpu mask for new SMP affinity
 246  *
 247  * This is executed in workqueue context.
 248  */
 249 static void
 250 irq_cpu_rmap_notify(struct irq_affinity_notify *notify, const cpumask_t *mask)
 251 {
 252         struct irq_glue *glue =
 253                 container_of(notify, struct irq_glue, notify);
 254         int rc;
 255
 256         rc = cpu_rmap_update(glue->rmap, glue->index, mask);
 257         if (rc)
 258                 pr_warn("irq_cpu_rmap_notify: update failed: %d\n", rc);
 259 }
 260
 261 /**
 262  * irq_cpu_rmap_release - reclaiming callback for IRQ subsystem
 263  * @ref: kref to struct irq_affinity_notify passed by irq/manage.c
 264  */
 265 static void irq_cpu_rmap_release(struct kref *ref)
 266 {
 267         struct irq_glue *glue =
 268                 container_of(ref, struct irq_glue, notify.kref);
 269
 270         cpu_rmap_put(glue->rmap);
 271         kfree(glue);
 272 }
 273
 274 /**
 275  * irq_cpu_rmap_add - add an IRQ to a CPU affinity reverse-map
 276  * @rmap: The reverse-map
 277  * @irq: The IRQ number
 278  *
 279  * This adds an IRQ affinity notifier that will update the reverse-map
 280  * automatically.
 281  *
 282  * Must be called in process context, after the IRQ is allocated but
 283  * before it is bound with request_irq().
 284  */
 285 int irq_cpu_rmap_add(struct cpu_rmap *rmap, int irq)
 286 {
 287         struct irq_glue *glue = kzalloc(sizeof(*glue), GFP_KERNEL);
 288         int rc;
 289
 290         if (!glue)
 291                 return -ENOMEM;
 292         glue->notify.notify = irq_cpu_rmap_notify;
 293         glue->notify.release = irq_cpu_rmap_release;
 294         glue->rmap = rmap;
 295         cpu_rmap_get(rmap);
 296         glue->index = cpu_rmap_add(rmap, glue);
 297         rc = irq_set_affinity_notifier(irq, &glue->notify);
 298         if (rc) {
 299                 cpu_rmap_put(glue->rmap);
 300                 kfree(glue);
 301         }
 302         return rc;
 303 }
 304 EXPORT_SYMBOL(irq_cpu_rmap_add);