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1// SPDX-License-Identifier: GPL-2.02/*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_SMP13 14static 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 45static 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 61out_unwind:62 while (--node >= 0)63 free_cpumask_var(masks[node]);64 kfree(masks);65 return NULL;66}67 68static 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 77static 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 85static 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 100struct node_groups {101 unsigned id;102 103 union {104 unsigned ngroups;105 unsigned ncpus;106 };107};108 109static 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 >= 1121 *122 * 2) the allocated number is <= active CPU number of this node123 *124 * The actual allocated total groups may be less than @numgrps when125 * 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 */130static 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 this163 * node's nr_cpus to remaining un-assigned ncpus. 'numgrps' is164 * bigger than number of active numa nodes. Always start the165 * allocation from the node with minimized nr_cpus.166 *167 * This way guarantees that each active node gets allocated at168 * least one group, and the theory is simple: over-allocation169 * is only done when this node is assigned by one group, so170 * other nodes will be allocated >= 1 groups, since 'numgrps' is171 * bigger than number of numa nodes.172 *173 * One perfect invariant is that number of allocated groups for174 * each node is <= CPU count of this node:175 *176 * 1) suppose there are two nodes: A and B177 * ncpu(X) is CPU count of node X178 * grps(X) is the group count allocated to node X via this179 * algorithm180 *181 * ncpu(A) <= ncpu(B)182 * ncpu(A) + ncpu(B) = N183 * grps(A) + grps(B) = G184 *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, suppose189 * G = N - delta, and 0 <= delta <= N - 2190 *191 * 2) obviously grps(A) <= ncpu(A) because:192 *193 * if grps(A) is 1, then grps(A) <= ncpu(A) given194 * ncpu(A) >= 1195 *196 * otherwise,197 * grps(A) <= G * ncpu(A) / N <= ncpu(A), given G <= N198 *199 * 3) prove how grps(B) <= ncpu(B):200 *201 * if round_down(G * ncpu(A) / N) == 0, vecs(B) won't be202 * 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) - delta212 *213 * then:214 *215 * grps(A) - G >= ncpu(A) - delta - G216 * =>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 big224 * node given that is exactly what this algorithm is implemented,225 * and we always re-calculate 'remaining_ncpus' & 'numgrps', and226 * 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 249static 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 the267 * 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 anywhere320 */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 locality334 * @numgrps: number of groups335 *336 * Return: cpumask array if successful, NULL otherwise. And each element337 * includes CPUs assigned to this group338 *339 * Try to put close CPUs from viewpoint of CPU and NUMA locality into340 * same group, and run two-stage grouping:341 * 1) allocate present CPUs on these groups evenly first342 * 2) allocate other possible CPUs on these groups evenly343 *344 * We guarantee in the resulted grouping that all CPUs are covered, and345 * no same CPU is assigned to multiple groups346 */347struct 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 stages373 * spread can observe consistent 'cpu_present_mask' without holding374 * cpu hotplug lock, then we can reduce deadlock risk with cpu375 * hotplug code.376 *377 * Here CPU hotplug may happen when reading `cpu_present_mask`, and378 * we can live with the case because it only affects that hotplug379 * CPU is handled in the 1st or 2nd stage, and either way is correct380 * from API user viewpoint since 2-stage spread is sort of381 * 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 be394 * handled. If the grouping of present CPUs already exhausted the395 * group space, assign the non present CPUs to the already396 * allocated out groups.397 */398 if (nr_present >= numgrps)399 curgrp = 0;400 else401 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 */427struct 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 */439EXPORT_SYMBOL_GPL(group_cpus_evenly);440