[linux.git] / lib / group_cpus.c

// 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;

	build_node_to_cpumask(node_to_cpumask);

	/*
	 * Make a local cache of 'cpu_present_mask', so the two stages
	 * spread can observe consistent 'cpu_present_mask' without holding
	 * cpu hotplug lock, then we can reduce deadlock risk with cpu
	 * hotplug code.
	 *
	 * Here CPU hotplug may happen when reading `cpu_present_mask`, and
	 * we can live with the case because it only affects that hotplug
	 * CPU is handled in the 1st or 2nd stage, and either way is correct
	 * from API user viewpoint since 2-stage spread is sort of
	 * optimization.
	 */
	cpumask_copy(npresmsk, data_race(cpu_present_mask));

	/* grouping present CPUs first */
	ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
				  npresmsk, 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, npresmsk);
	ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
				  npresmsk, nmsk, masks);
	if (ret >= 0)
		nr_others = ret;

 fail_build_affinity:
	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 */
EXPORT_SYMBOL_GPL(group_cpus_evenly);
Commit	Line	Data
f7b3ea8c ML	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
188a5696 IM	12	#ifdef CONFIG_SMP
188a5696 IM	13
f7b3ea8c ML	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
f7b3ea8c ML	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
f7b3ea8c ML	369	build_node_to_cpumask(node_to_cpumask);
f7b3ea8c ML	370
0263f92f ML	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
f7b3ea8c ML	385	/* grouping present CPUs first */
f7b3ea8c ML	386	ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
0263f92f	387	npresmsk, nmsk, masks);
f7b3ea8c ML	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;
0263f92f	402	cpumask_andnot(npresmsk, cpu_possible_mask, npresmsk);
f7b3ea8c ML	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:
f7b3ea8c ML	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	}
188a5696	426	#else /* CONFIG_SMP */
f7b3ea8c ML	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	}
188a5696	438	#endif /* CONFIG_SMP */
aaf05948	439	EXPORT_SYMBOL_GPL(group_cpus_evenly);