// 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);
