summaryrefslogtreecommitdiffstats
path: root/lib/group_cpus.c
blob: 9c837a35fef7bf375fc68ea5083303bf4c095a3b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2016 Thomas Gleixner.
 * Copyright (C) 2016-2017 Christoph Hellwig.
 */
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/sort.h>
#include <linux/group_cpus.h>

#ifdef CONFIG_SMP

static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
				unsigned int cpus_per_grp)
{
	const struct cpumask *siblmsk;
	int cpu, sibl;

	for ( ; cpus_per_grp > 0; ) {
		cpu = cpumask_first(nmsk);

		/* Should not happen, but I'm too lazy to think about it */
		if (cpu >= nr_cpu_ids)
			return;

		cpumask_clear_cpu(cpu, nmsk);
		cpumask_set_cpu(cpu, irqmsk);
		cpus_per_grp--;

		/* If the cpu has siblings, use them first */
		siblmsk = topology_sibling_cpumask(cpu);
		for (sibl = -1; cpus_per_grp > 0; ) {
			sibl = cpumask_next(sibl, siblmsk);
			if (sibl >= nr_cpu_ids)
				break;
			if (!cpumask_test_and_clear_cpu(sibl, nmsk))
				continue;
			cpumask_set_cpu(sibl, irqmsk);
			cpus_per_grp--;
		}
	}
}

static cpumask_var_t *alloc_node_to_cpumask(void)
{
	cpumask_var_t *masks;
	int node;

	masks = kcalloc(nr_node_ids, sizeof(cpumask_var_t), GFP_KERNEL);
	if (!masks)
		return NULL;

	for (node = 0; node < nr_node_ids; node++) {
		if (!zalloc_cpumask_var(&masks[node], GFP_KERNEL))
			goto out_unwind;
	}

	return masks;

out_unwind:
	while (--node >= 0)
		free_cpumask_var(masks[node]);
	kfree(masks);
	return NULL;
}

static void free_node_to_cpumask(cpumask_var_t *masks)
{
	int node;

	for (node = 0; node < nr_node_ids; node++)
		free_cpumask_var(masks[node]);
	kfree(masks);
}

static void build_node_to_cpumask(cpumask_var_t *masks)
{
	int cpu;

	for_each_possible_cpu(cpu)
		cpumask_set_cpu(cpu, masks[cpu_to_node(cpu)]);
}

static int get_nodes_in_cpumask(cpumask_var_t *node_to_cpumask,
				const struct cpumask *mask, nodemask_t *nodemsk)
{
	int n, nodes = 0;

	/* Calculate the number of nodes in the supplied affinity mask */
	for_each_node(n) {
		if (cpumask_intersects(mask, node_to_cpumask[n])) {
			node_set(n, *nodemsk);
			nodes++;
		}
	}
	return nodes;
}

struct node_groups {
	unsigned id;

	union {
		unsigned ngroups;
		unsigned ncpus;
	};
};

static int ncpus_cmp_func(const void *l, const void *r)
{
	const struct node_groups *ln = l;
	const struct node_groups *rn = r;

	return ln->ncpus - rn->ncpus;
}

/*
 * Allocate group number for each node, so that for each node:
 *
 * 1) the allocated number is >= 1
 *
 * 2) the allocated number is <= active CPU number of this node
 *
 * The actual allocated total groups may be less than @numgrps when
 * active total CPU number is less than @numgrps.
 *
 * Active CPUs means the CPUs in '@cpu_mask AND @node_to_cpumask[]'
 * for each node.
 */
static void alloc_nodes_groups(unsigned int numgrps,
			       cpumask_var_t *node_to_cpumask,
			       const struct cpumask *cpu_mask,
			       const nodemask_t nodemsk,
			       struct cpumask *nmsk,
			       struct node_groups *node_groups)
{
	unsigned n, remaining_ncpus = 0;

	for (n = 0; n < nr_node_ids; n++) {
		node_groups[n].id = n;
		node_groups[n].ncpus = UINT_MAX;
	}

	for_each_node_mask(n, nodemsk) {
		unsigned ncpus;

		cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
		ncpus = cpumask_weight(nmsk);

		if (!ncpus)
			continue;
		remaining_ncpus += ncpus;
		node_groups[n].ncpus = ncpus;
	}

	numgrps = min_t(unsigned, remaining_ncpus, numgrps);

	sort(node_groups, nr_node_ids, sizeof(node_groups[0]),
	     ncpus_cmp_func, NULL);

	/*
	 * Allocate groups for each node according to the ratio of this
	 * node's nr_cpus to remaining un-assigned ncpus. 'numgrps' is
	 * bigger than number of active numa nodes. Always start the
	 * allocation from the node with minimized nr_cpus.
	 *
	 * This way guarantees that each active node gets allocated at
	 * least one group, and the theory is simple: over-allocation
	 * is only done when this node is assigned by one group, so
	 * other nodes will be allocated >= 1 groups, since 'numgrps' is
	 * bigger than number of numa nodes.
	 *
	 * One perfect invariant is that number of allocated groups for
	 * each node is <= CPU count of this node:
	 *
	 * 1) suppose there are two nodes: A and B
	 * 	ncpu(X) is CPU count of node X
	 * 	grps(X) is the group count allocated to node X via this
	 * 	algorithm
	 *
	 * 	ncpu(A) <= ncpu(B)
	 * 	ncpu(A) + ncpu(B) = N
	 * 	grps(A) + grps(B) = G
	 *
	 * 	grps(A) = max(1, round_down(G * ncpu(A) / N))
	 * 	grps(B) = G - grps(A)
	 *
	 * 	both N and G are integer, and 2 <= G <= N, suppose
	 * 	G = N - delta, and 0 <= delta <= N - 2
	 *
	 * 2) obviously grps(A) <= ncpu(A) because:
	 *
	 * 	if grps(A) is 1, then grps(A) <= ncpu(A) given
	 * 	ncpu(A) >= 1
	 *
	 * 	otherwise,
	 * 		grps(A) <= G * ncpu(A) / N <= ncpu(A), given G <= N
	 *
	 * 3) prove how grps(B) <= ncpu(B):
	 *
	 * 	if round_down(G * ncpu(A) / N) == 0, vecs(B) won't be
	 * 	over-allocated, so grps(B) <= ncpu(B),
	 *
	 * 	otherwise:
	 *
	 * 	grps(A) =
	 * 		round_down(G * ncpu(A) / N) =
	 * 		round_down((N - delta) * ncpu(A) / N) =
	 * 		round_down((N * ncpu(A) - delta * ncpu(A)) / N)	 >=
	 * 		round_down((N * ncpu(A) - delta * N) / N)	 =
	 * 		cpu(A) - delta
	 *
	 * 	then:
	 *
	 * 	grps(A) - G >= ncpu(A) - delta - G
	 * 	=>
	 * 	G - grps(A) <= G + delta - ncpu(A)
	 * 	=>
	 * 	grps(B) <= N - ncpu(A)
	 * 	=>
	 * 	grps(B) <= cpu(B)
	 *
	 * For nodes >= 3, it can be thought as one node and another big
	 * node given that is exactly what this algorithm is implemented,
	 * and we always re-calculate 'remaining_ncpus' & 'numgrps', and
	 * finally for each node X: grps(X) <= ncpu(X).
	 *
	 */
	for (n = 0; n < nr_node_ids; n++) {
		unsigned ngroups, ncpus;

		if (node_groups[n].ncpus == UINT_MAX)
			continue;

		WARN_ON_ONCE(numgrps == 0);

		ncpus = node_groups[n].ncpus;
		ngroups = max_t(unsigned, 1,
				 numgrps * ncpus / remaining_ncpus);
		WARN_ON_ONCE(ngroups > ncpus);

		node_groups[n].ngroups = ngroups;

		remaining_ncpus -= ncpus;
		numgrps -= ngroups;
	}
}

static int __group_cpus_evenly(unsigned int startgrp, unsigned int numgrps,
			       cpumask_var_t *node_to_cpumask,
			       const struct cpumask *cpu_mask,
			       struct cpumask *nmsk, struct cpumask *masks)
{
	unsigned int i, n, nodes, cpus_per_grp, extra_grps, done = 0;
	unsigned int last_grp = numgrps;
	unsigned int curgrp = startgrp;
	nodemask_t nodemsk = NODE_MASK_NONE;
	struct node_groups *node_groups;

	if (cpumask_empty(cpu_mask))
		return 0;

	nodes = get_nodes_in_cpumask(node_to_cpumask, cpu_mask, &nodemsk);

	/*
	 * If the number of nodes in the mask is greater than or equal the
	 * number of groups we just spread the groups across the nodes.
	 */
	if (numgrps <= nodes) {
		for_each_node_mask(n, nodemsk) {
			/* Ensure that only CPUs which are in both masks are set */
			cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
			cpumask_or(&masks[curgrp], &masks[curgrp], nmsk);
			if (++curgrp == last_grp)
				curgrp = 0;
		}
		return numgrps;
	}

	node_groups = kcalloc(nr_node_ids,
			       sizeof(struct node_groups),
			       GFP_KERNEL);
	if (!node_groups)
		return -ENOMEM;

	/* allocate group number for each node */
	alloc_nodes_groups(numgrps, node_to_cpumask, cpu_mask,
			   nodemsk, nmsk, node_groups);
	for (i = 0; i < nr_node_ids; i++) {
		unsigned int ncpus, v;
		struct node_groups *nv = &node_groups[i];

		if (nv->ngroups == UINT_MAX)
			continue;

		/* Get the cpus on this node which are in the mask */
		cpumask_and(nmsk, cpu_mask, node_to_cpumask[nv->id]);
		ncpus = cpumask_weight(nmsk);
		if (!ncpus)
			continue;

		WARN_ON_ONCE(nv->ngroups > ncpus);

		/* Account for rounding errors */
		extra_grps = ncpus - nv->ngroups * (ncpus / nv->ngroups);

		/* Spread allocated groups on CPUs of the current node */
		for (v = 0; v < nv->ngroups; v++, curgrp++) {
			cpus_per_grp = ncpus / nv->ngroups;

			/* Account for extra groups to compensate rounding errors */
			if (extra_grps) {
				cpus_per_grp++;
				--extra_grps;
			}

			/*
			 * wrapping has to be considered given 'startgrp'
			 * may start anywhere
			 */
			if (curgrp >= last_grp)
				curgrp = 0;
			grp_spread_init_one(&masks[curgrp], nmsk,
						cpus_per_grp);
		}
		done += nv->ngroups;
	}
	kfree(node_groups);
	return done;
}

/**
 * group_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
 * @numgrps: number of groups
 *
 * Return: cpumask array if successful, NULL otherwise. And each element
 * includes CPUs assigned to this group
 *
 * Try to put close CPUs from viewpoint of CPU and NUMA locality into
 * same group, and run two-stage grouping:
 *	1) allocate present CPUs on these groups evenly first
 *	2) allocate other possible CPUs on these groups evenly
 *
 * We guarantee in the resulted grouping that all CPUs are covered, and
 * no same CPU is assigned to multiple groups
 */
struct cpumask *group_cpus_evenly(unsigned int numgrps)
{
	unsigned int curgrp = 0, nr_present = 0, nr_others = 0;
	cpumask_var_t *node_to_cpumask;
	cpumask_var_t nmsk, npresmsk;
	int ret = -ENOMEM;
	struct cpumask *masks = NULL;

	if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
		return NULL;

	if (!zalloc_cpumask_var(&npresmsk, GFP_KERNEL))
		goto fail_nmsk;

	node_to_cpumask = alloc_node_to_cpumask();
	if (!node_to_cpumask)
		goto fail_npresmsk;

	masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);
	if (!masks)
		goto fail_node_to_cpumask;

	/* Stabilize the cpumasks */
	cpus_read_lock();
	build_node_to_cpumask(node_to_cpumask);

	/* grouping present CPUs first */
	ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
				  cpu_present_mask, nmsk, masks);
	if (ret < 0)
		goto fail_build_affinity;
	nr_present = ret;

	/*
	 * Allocate non present CPUs starting from the next group to be
	 * handled. If the grouping of present CPUs already exhausted the
	 * group space, assign the non present CPUs to the already
	 * allocated out groups.
	 */
	if (nr_present >= numgrps)
		curgrp = 0;
	else
		curgrp = nr_present;
	cpumask_andnot(npresmsk, cpu_possible_mask, cpu_present_mask);
	ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
				  npresmsk, nmsk, masks);
	if (ret >= 0)
		nr_others = ret;

 fail_build_affinity:
	cpus_read_unlock();

	if (ret >= 0)
		WARN_ON(nr_present + nr_others < numgrps);

 fail_node_to_cpumask:
	free_node_to_cpumask(node_to_cpumask);

 fail_npresmsk:
	free_cpumask_var(npresmsk);

 fail_nmsk:
	free_cpumask_var(nmsk);
	if (ret < 0) {
		kfree(masks);
		return NULL;
	}
	return masks;
}
#else /* CONFIG_SMP */
struct cpumask *group_cpus_evenly(unsigned int numgrps)
{
	struct cpumask *masks = kcalloc(numgrps, sizeof(*masks), GFP_KERNEL);

	if (!masks)
		return NULL;

	/* assign all CPUs(cpu 0) to the 1st group only */
	cpumask_copy(&masks[0], cpu_possible_mask);
	return masks;
}
#endif /* CONFIG_SMP */