lib/group_cpus.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2016 Thomas Gleixner.
   4  * Copyright (C) 2016-2017 Christoph Hellwig.
   5  */
   6 #include <linux/kernel.h>
   7 #include <linux/slab.h>
   8 #include <linux/cpu.h>
   9 #include <linux/sort.h>
  10 #include <linux/group_cpus.h>
  11
  12 #ifdef CONFIG_SMP
  13
  14 static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
  15                                 unsigned int cpus_per_grp)
  16 {
  17         const struct cpumask *siblmsk;
  18         int cpu, sibl;
  19
  20         for ( ; cpus_per_grp > 0; ) {
  21                 cpu = cpumask_first(nmsk);
  22
  23                 /* Should not happen, but I'm too lazy to think about it */
  24                 if (cpu >= nr_cpu_ids)
  25                         return;
  26
  27                 cpumask_clear_cpu(cpu, nmsk);
  28                 cpumask_set_cpu(cpu, irqmsk);
  29                 cpus_per_grp--;
  30
  31                 /* If the cpu has siblings, use them first */
  32                 siblmsk = topology_sibling_cpumask(cpu);
  33                 for (sibl = -1; cpus_per_grp > 0; ) {
  34                         sibl = cpumask_next(sibl, siblmsk);
  35                         if (sibl >= nr_cpu_ids)
  36                                 break;
  37                         if (!cpumask_test_and_clear_cpu(sibl, nmsk))
  38                                 continue;
  39                         cpumask_set_cpu(sibl, irqmsk);
  40                         cpus_per_grp--;
  41                 }
  42         }
  43 }
  44
  45 static cpumask_var_t *alloc_node_to_cpumask(void)
  46 {
  47         cpumask_var_t *masks;
  48         int node;
  49
  50         masks = kcalloc(nr_node_ids, sizeof(cpumask_var_t), GFP_KERNEL);
  51         if (!masks)
  52                 return NULL;
  53
  54         for (node = 0; node < nr_node_ids; node++) {
  55                 if (!zalloc_cpumask_var(&masks[node], GFP_KERNEL))
  56                         goto out_unwind;
  57         }
  58
  59         return masks;
  60
  61 out_unwind:
  62         while (--node >= 0)
  63                 free_cpumask_var(masks[node]);
  64         kfree(masks);
  65         return NULL;
  66 }
  67
  68 static void free_node_to_cpumask(cpumask_var_t *masks)
  69 {
  70         int node;
  71
  72         for (node = 0; node < nr_node_ids; node++)
  73                 free_cpumask_var(masks[node]);
  74         kfree(masks);
  75 }
  76
  77 static void build_node_to_cpumask(cpumask_var_t *masks)
  78 {
  79         int cpu;
  80
  81         for_each_possible_cpu(cpu)
  82                 cpumask_set_cpu(cpu, masks[cpu_to_node(cpu)]);
  83 }
  84
  85 static int get_nodes_in_cpumask(cpumask_var_t *node_to_cpumask,
  86                                 const struct cpumask *mask, nodemask_t *nodemsk)
  87 {
  88         int n, nodes = 0;
  89
  90         /* Calculate the number of nodes in the supplied affinity mask */
  91         for_each_node(n) {
  92                 if (cpumask_intersects(mask, node_to_cpumask[n])) {
  93                         node_set(n, *nodemsk);
  94                         nodes++;
  95                 }
  96         }
  97         return nodes;
  98 }
  99
 100 struct node_groups {
 101         unsigned id;
 102
 103         union {
 104                 unsigned ngroups;
 105                 unsigned ncpus;
 106         };
 107 };
 108
 109 static int ncpus_cmp_func(const void *l, const void *r)
 110 {
 111         const struct node_groups *ln = l;
 112         const struct node_groups *rn = r;
 113
 114         return ln->ncpus - rn->ncpus;
 115 }
 116
 117 /*
 118  * Allocate group number for each node, so that for each node:
 119  *
 120  * 1) the allocated number is >= 1
 121  *
 122  * 2) the allocated number is <= active CPU number of this node
 123  *
 124  * The actual allocated total groups may be less than @numgrps when
 125  * active total CPU number is less than @numgrps.
 126  *
 127  * Active CPUs means the CPUs in '@cpu_mask AND @node_to_cpumask[]'
 128  * for each node.
 129  */
 130 static void alloc_nodes_groups(unsigned int numgrps,
 131                                cpumask_var_t *node_to_cpumask,
 132                                const struct cpumask *cpu_mask,
 133                                const nodemask_t nodemsk,
 134                                struct cpumask *nmsk,
 135                                struct node_groups *node_groups)
 136 {
 137         unsigned n, remaining_ncpus = 0;
 138
 139         for (n = 0; n < nr_node_ids; n++) {
 140                 node_groups[n].id = n;
 141                 node_groups[n].ncpus = UINT_MAX;
 142         }
 143
 144         for_each_node_mask(n, nodemsk) {
 145                 unsigned ncpus;
 146
 147                 cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
 148                 ncpus = cpumask_weight(nmsk);
 149
 150                 if (!ncpus)
 151                         continue;
 152                 remaining_ncpus += ncpus;
 153                 node_groups[n].ncpus = ncpus;
 154         }
 155
 156         numgrps = min_t(unsigned, remaining_ncpus, numgrps);
 157
 158         sort(node_groups, nr_node_ids, sizeof(node_groups[0]),
 159              ncpus_cmp_func, NULL);
 160
 161         /*
 162          * Allocate groups for each node according to the ratio of this
 163          * node's nr_cpus to remaining un-assigned ncpus. 'numgrps' is
 164          * bigger than number of active numa nodes. Always start the
 165          * allocation from the node with minimized nr_cpus.
 166          *
 167          * This way guarantees that each active node gets allocated at
 168          * least one group, and the theory is simple: over-allocation
 169          * is only done when this node is assigned by one group, so
 170          * other nodes will be allocated >= 1 groups, since 'numgrps' is
 171          * bigger than number of numa nodes.
 172          *
 173          * One perfect invariant is that number of allocated groups for
 174          * each node is <= CPU count of this node:
 175          *
 176          * 1) suppose there are two nodes: A and B
 177          *      ncpu(X) is CPU count of node X
 178          *      grps(X) is the group count allocated to node X via this
 179          *      algorithm
 180          *
 181          *      ncpu(A) <= ncpu(B)
 182          *      ncpu(A) + ncpu(B) = N
 183          *      grps(A) + grps(B) = G
 184          *
 185          *      grps(A) = max(1, round_down(G * ncpu(A) / N))
 186          *      grps(B) = G - grps(A)
 187          *
 188          *      both N and G are integer, and 2 <= G <= N, suppose
 189          *      G = N - delta, and 0 <= delta <= N - 2
 190          *
 191          * 2) obviously grps(A) <= ncpu(A) because:
 192          *
 193          *      if grps(A) is 1, then grps(A) <= ncpu(A) given
 194          *      ncpu(A) >= 1
 195          *
 196          *      otherwise,
 197          *              grps(A) <= G * ncpu(A) / N <= ncpu(A), given G <= N
 198          *
 199          * 3) prove how grps(B) <= ncpu(B):
 200          *
 201          *      if round_down(G * ncpu(A) / N) == 0, vecs(B) won't be
 202          *      over-allocated, so grps(B) <= ncpu(B),
 203          *
 204          *      otherwise:
 205          *
 206          *      grps(A) =
 207          *              round_down(G * ncpu(A) / N) =
 208          *              round_down((N - delta) * ncpu(A) / N) =
 209          *              round_down((N * ncpu(A) - delta * ncpu(A)) / N)  >=
 210          *              round_down((N * ncpu(A) - delta * N) / N)        =
 211          *              cpu(A) - delta
 212          *
 213          *      then:
 214          *
 215          *      grps(A) - G >= ncpu(A) - delta - G
 216          *      =>
 217          *      G - grps(A) <= G + delta - ncpu(A)
 218          *      =>
 219          *      grps(B) <= N - ncpu(A)
 220          *      =>
 221          *      grps(B) <= cpu(B)
 222          *
 223          * For nodes >= 3, it can be thought as one node and another big
 224          * node given that is exactly what this algorithm is implemented,
 225          * and we always re-calculate 'remaining_ncpus' & 'numgrps', and
 226          * finally for each node X: grps(X) <= ncpu(X).
 227          *
 228          */
 229         for (n = 0; n < nr_node_ids; n++) {
 230                 unsigned ngroups, ncpus;
 231
 232                 if (node_groups[n].ncpus == UINT_MAX)
 233                         continue;
 234
 235                 WARN_ON_ONCE(numgrps == 0);
 236
 237                 ncpus = node_groups[n].ncpus;
 238                 ngroups = max_t(unsigned, 1,
 239                                  numgrps * ncpus / remaining_ncpus);
 240                 WARN_ON_ONCE(ngroups > ncpus);
 241
 242                 node_groups[n].ngroups = ngroups;
 243
 244                 remaining_ncpus -= ncpus;
 245                 numgrps -= ngroups;
 246         }
 247 }
 248
 249 static int __group_cpus_evenly(unsigned int startgrp, unsigned int numgrps,
 250                                cpumask_var_t *node_to_cpumask,
 251                                const struct cpumask *cpu_mask,
 252                                struct cpumask *nmsk, struct cpumask *masks)
 253 {
 254         unsigned int i, n, nodes, cpus_per_grp, extra_grps, done = 0;
 255         unsigned int last_grp = numgrps;
 256         unsigned int curgrp = startgrp;
 257         nodemask_t nodemsk = NODE_MASK_NONE;
 258         struct node_groups *node_groups;
 259
 260         if (cpumask_empty(cpu_mask))
 261                 return 0;
 262
 263         nodes = get_nodes_in_cpumask(node_to_cpumask, cpu_mask, &nodemsk);
 264
 265         /*
 266          * If the number of nodes in the mask is greater than or equal the
 267          * number of groups we just spread the groups across the nodes.
 268          */
 269         if (numgrps <= nodes) {
 270                 for_each_node_mask(n, nodemsk) {
 271                         /* Ensure that only CPUs which are in both masks are set */
 272                         cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
 273                         cpumask_or(&masks[curgrp], &masks[curgrp], nmsk);
 274                         if (++curgrp == last_grp)
 275                                 curgrp = 0;
 276                 }
 277                 return numgrps;
 278         }
 279
 280         node_groups = kcalloc(nr_node_ids,
 281                                sizeof(struct node_groups),
 282                                GFP_KERNEL);
 283         if (!node_groups)
 284                 return -ENOMEM;
 285
 286         /* allocate group number for each node */
 287         alloc_nodes_groups(numgrps, node_to_cpumask, cpu_mask,
 288                            nodemsk, nmsk, node_groups);
 289         for (i = 0; i < nr_node_ids; i++) {
 290                 unsigned int ncpus, v;
 291                 struct node_groups *nv = &node_groups[i];
 292
 293                 if (nv->ngroups == UINT_MAX)
 294                         continue;
 295
 296                 /* Get the cpus on this node which are in the mask */
 297                 cpumask_and(nmsk, cpu_mask, node_to_cpumask[nv->id]);
 298                 ncpus = cpumask_weight(nmsk);
 299                 if (!ncpus)
 300                         continue;
 301
 302                 WARN_ON_ONCE(nv->ngroups > ncpus);
 303
 304                 /* Account for rounding errors */
 305                 extra_grps = ncpus - nv->ngroups * (ncpus / nv->ngroups);
 306
 307                 /* Spread allocated groups on CPUs of the current node */
 308                 for (v = 0; v < nv->ngroups; v++, curgrp++) {
 309                         cpus_per_grp = ncpus / nv->ngroups;
 310
 311                         /* Account for extra groups to compensate rounding errors */
 312                         if (extra_grps) {
 313                                 cpus_per_grp++;
 314                                 --extra_grps;
 315                         }
 316
 317                         /*
 318                          * wrapping has to be considered given 'startgrp'
 319                          * may start anywhere
 320                          */
 321                         if (curgrp >= last_grp)
 322                                 curgrp = 0;
 323                         grp_spread_init_one(&masks[curgrp], nmsk,
 324                                                 cpus_per_grp);
 325                 }
 326                 done += nv->ngroups;
 327         }
 328         kfree(node_groups);
 329         return done;
 330 }
 331
 332 /**
 333  * group_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
 334  * @numgrps: number of groups
 335  *
 336  * Return: cpumask array if successful, NULL otherwise. And each element
 337  * includes CPUs assigned to this group
 338  *
 339  * Try to put close CPUs from viewpoint of CPU and NUMA locality into
 340  * same group, and run two-stage grouping:
 341  *      1) allocate present CPUs on these groups evenly first
 342  *      2) allocate other possible CPUs on these groups evenly
 343  *
 344  * We guarantee in the resulted grouping that all CPUs are covered, and
 345  * no same CPU is assigned to multiple groups
 346  */
 347 struct cpumask *group_cpus_evenly(unsigned int numgrps)
 348 {
 349         unsigned int curgrp = 0, nr_present = 0, nr_others = 0;
 350         cpumask_var_t *node_to_cpumask;
 351         cpumask_var_t nmsk, npresmsk;
 352         int ret = -ENOMEM;
 353         struct cpumask *masks = NULL;
 354
 355         if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
 356                 return NULL;
 357
 358         if (!zalloc_cpumask_var(&npresmsk, GFP_KERNEL))
 359                 goto fail_nmsk;
 360
 361         node_to_cpumask = alloc_node_to_cpumask();
 362         if (!node_to_cpumask)
 363                 goto fail_npresmsk;
 364
 365         masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);
 366         if (!masks)
 367                 goto fail_node_to_cpumask;
 368
 369         build_node_to_cpumask(node_to_cpumask);
 370
 371         /*
 372          * Make a local cache of 'cpu_present_mask', so the two stages
 373          * spread can observe consistent 'cpu_present_mask' without holding
 374          * cpu hotplug lock, then we can reduce deadlock risk with cpu
 375          * hotplug code.
 376          *
 377          * Here CPU hotplug may happen when reading `cpu_present_mask`, and
 378          * we can live with the case because it only affects that hotplug
 379          * CPU is handled in the 1st or 2nd stage, and either way is correct
 380          * from API user viewpoint since 2-stage spread is sort of
 381          * optimization.
 382          */
 383         cpumask_copy(npresmsk, data_race(cpu_present_mask));
 384
 385         /* grouping present CPUs first */
 386         ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
 387                                   npresmsk, nmsk, masks);
 388         if (ret < 0)
 389                 goto fail_build_affinity;
 390         nr_present = ret;
 391
 392         /*
 393          * Allocate non present CPUs starting from the next group to be
 394          * handled. If the grouping of present CPUs already exhausted the
 395          * group space, assign the non present CPUs to the already
 396          * allocated out groups.
 397          */
 398         if (nr_present >= numgrps)
 399                 curgrp = 0;
 400         else
 401                 curgrp = nr_present;
 402         cpumask_andnot(npresmsk, cpu_possible_mask, npresmsk);
 403         ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
 404                                   npresmsk, nmsk, masks);
 405         if (ret >= 0)
 406                 nr_others = ret;
 407
 408  fail_build_affinity:
 409         if (ret >= 0)
 410                 WARN_ON(nr_present + nr_others < numgrps);
 411
 412  fail_node_to_cpumask:
 413         free_node_to_cpumask(node_to_cpumask);
 414
 415  fail_npresmsk:
 416         free_cpumask_var(npresmsk);
 417
 418  fail_nmsk:
 419         free_cpumask_var(nmsk);
 420         if (ret < 0) {
 421                 kfree(masks);
 422                 return NULL;
 423         }
 424         return masks;
 425 }
 426 #else /* CONFIG_SMP */
 427 struct cpumask *group_cpus_evenly(unsigned int numgrps)
 428 {
 429         struct cpumask *masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);
 430
 431         if (!masks)
 432                 return NULL;
 433
 434         /* assign all CPUs(cpu 0) to the 1st group only */
 435         cpumask_copy(&masks[0], cpu_possible_mask);
 436         return masks;
 437 }
 438 #endif /* CONFIG_SMP */
 439 EXPORT_SYMBOL_GPL(group_cpus_evenly);