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);
440
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