1 files changed, 438 insertions, 0 deletions

diff --git a/lib/group_cpus.c b/lib/group_cpus.c
new file mode 100644
index 000000000..029261190
--- /dev/null
+++ b/lib/group_cpus.c
@@ -0,0 +1,438 @@
+// 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 */