lib/group_cpus.c - linux/kernel/git/gregkh/driver-core - Git at Google

 // 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);
	// 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);