genirq/affinity: Consider that CPUs on nodes can be unbalanced

[mirror_ubuntu-jammy-kernel.git] / kernel / irq / affinity.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2016 Thomas Gleixner.
 * Copyright (C) 2016-2017 Christoph Hellwig.
 */
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/sort.h>

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

        for ( ; cpus_per_vec > 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_vec--;

                /* If the cpu has siblings, use them first */
                siblmsk = topology_sibling_cpumask(cpu);
                for (sibl = -1; cpus_per_vec > 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_vec--;
                }
        }
}

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_vectors {
        unsigned id;

        union {
                unsigned nvectors;
                unsigned ncpus;
        };
};

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

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

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

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

        numvecs = min_t(unsigned, remaining_ncpus, numvecs);

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

        /*
         * Allocate vectors for each node according to the ratio of this
         * node's nr_cpus to remaining un-assigned ncpus. 'numvecs' 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 vector, and the theory is simple: over-allocation
         * is only done when this node is assigned by one vector, so
         * other nodes will be allocated >= 1 vector, since 'numvecs' is
         * bigger than number of numa nodes.
         *
         * One perfect invariant is that number of allocated vectors 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
         *      vecs(X) is the vector count allocated to node X via this
         *      algorithm
         *
         *      ncpu(A) <= ncpu(B)
         *      ncpu(A) + ncpu(B) = N
         *      vecs(A) + vecs(B) = V
         *
         *      vecs(A) = max(1, round_down(V * ncpu(A) / N))
         *      vecs(B) = V - vecs(A)
         *
         *      both N and V are integer, and 2 <= V <= N, suppose
         *      V = N - delta, and 0 <= delta <= N - 2
         *
         * 2) obviously vecs(A) <= ncpu(A) because:
         *
         *      if vecs(A) is 1, then vecs(A) <= ncpu(A) given
         *      ncpu(A) >= 1
         *
         *      otherwise,
         *              vecs(A) <= V * ncpu(A) / N <= ncpu(A), given V <= N
         *
         * 3) prove how vecs(B) <= ncpu(B):
         *
         *      if round_down(V * ncpu(A) / N) == 0, vecs(B) won't be
         *      over-allocated, so vecs(B) <= ncpu(B),
         *
         *      otherwise:
         *
         *      vecs(A) =
         *              round_down(V * 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:
         *
         *      vecs(A) - V >= ncpu(A) - delta - V
         *      =>
         *      V - vecs(A) <= V + delta - ncpu(A)
         *      =>
         *      vecs(B) <= N - ncpu(A)
         *      =>
         *      vecs(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' & 'numvecs', and
         * finally for each node X: vecs(X) <= ncpu(X).
         *
         */
        for (n = 0; n < nr_node_ids; n++) {
                unsigned nvectors, ncpus;

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

                WARN_ON_ONCE(numvecs == 0);

                ncpus = node_vectors[n].ncpus;
                nvectors = max_t(unsigned, 1,
                                 numvecs * ncpus / remaining_ncpus);
                WARN_ON_ONCE(nvectors > ncpus);

                node_vectors[n].nvectors = nvectors;

                remaining_ncpus -= ncpus;
                numvecs -= nvectors;
        }
}

static int __irq_build_affinity_masks(unsigned int startvec,
                                      unsigned int numvecs,
                                      unsigned int firstvec,
                                      cpumask_var_t *node_to_cpumask,
                                      const struct cpumask *cpu_mask,
                                      struct cpumask *nmsk,
                                      struct irq_affinity_desc *masks)
{
        unsigned int i, n, nodes, cpus_per_vec, extra_vecs, done = 0;
        unsigned int last_affv = firstvec + numvecs;
        unsigned int curvec = startvec;
        nodemask_t nodemsk = NODE_MASK_NONE;
        struct node_vectors *node_vectors;

        if (!cpumask_weight(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 vectors we just spread the vectors across the nodes.
         */
        if (numvecs <= 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[curvec].mask, &masks[curvec].mask, nmsk);
                        if (++curvec == last_affv)
                                curvec = firstvec;
                }
                return numvecs;
        }

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

        /* allocate vector number for each node */
        alloc_nodes_vectors(numvecs, node_to_cpumask, cpu_mask,
                            nodemsk, nmsk, node_vectors);

        for (i = 0; i < nr_node_ids; i++) {
                unsigned int ncpus, v;
                struct node_vectors *nv = &node_vectors[i];

                if (nv->nvectors == 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->nvectors > ncpus);

                /* Account for rounding errors */
                extra_vecs = ncpus - nv->nvectors * (ncpus / nv->nvectors);

                /* Spread allocated vectors on CPUs of the current node */
                for (v = 0; v < nv->nvectors; v++, curvec++) {
                        cpus_per_vec = ncpus / nv->nvectors;

                        /* Account for extra vectors to compensate rounding errors */
                        if (extra_vecs) {
                                cpus_per_vec++;
                                --extra_vecs;
                        }

                        /*
                         * wrapping has to be considered given 'startvec'
                         * may start anywhere
                         */
                        if (curvec >= last_affv)
                                curvec = firstvec;
                        irq_spread_init_one(&masks[curvec].mask, nmsk,
                                                cpus_per_vec);
                }
                done += nv->nvectors;
        }
        kfree(node_vectors);
        return done;
}

/*
 * build affinity in two stages:
 *      1) spread present CPU on these vectors
 *      2) spread other possible CPUs on these vectors
 */
static int irq_build_affinity_masks(unsigned int startvec, unsigned int numvecs,
                                    unsigned int firstvec,
                                    struct irq_affinity_desc *masks)
{
        unsigned int curvec = startvec, nr_present = 0, nr_others = 0;
        cpumask_var_t *node_to_cpumask;
        cpumask_var_t nmsk, npresmsk;
        int ret = -ENOMEM;

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

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

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

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

        /* Spread on present CPUs starting from affd->pre_vectors */
        ret = __irq_build_affinity_masks(curvec, numvecs, firstvec,
                                         node_to_cpumask, cpu_present_mask,
                                         nmsk, masks);
        if (ret < 0)
                goto fail_build_affinity;
        nr_present = ret;

        /*
         * Spread on non present CPUs starting from the next vector to be
         * handled. If the spreading of present CPUs already exhausted the
         * vector space, assign the non present CPUs to the already spread
         * out vectors.
         */
        if (nr_present >= numvecs)
                curvec = firstvec;
        else
                curvec = firstvec + nr_present;
        cpumask_andnot(npresmsk, cpu_possible_mask, cpu_present_mask);
        ret = __irq_build_affinity_masks(curvec, numvecs, firstvec,
                                         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 < numvecs);

        free_node_to_cpumask(node_to_cpumask);

 fail_npresmsk:
        free_cpumask_var(npresmsk);

 fail_nmsk:
        free_cpumask_var(nmsk);
        return ret < 0 ? ret : 0;
}

static void default_calc_sets(struct irq_affinity *affd, unsigned int affvecs)
{
        affd->nr_sets = 1;
        affd->set_size[0] = affvecs;
}

/**
 * irq_create_affinity_masks - Create affinity masks for multiqueue spreading
 * @nvecs:      The total number of vectors
 * @affd:       Description of the affinity requirements
 *
 * Returns the irq_affinity_desc pointer or NULL if allocation failed.
 */
struct irq_affinity_desc *
irq_create_affinity_masks(unsigned int nvecs, struct irq_affinity *affd)
{
        unsigned int affvecs, curvec, usedvecs, i;
        struct irq_affinity_desc *masks = NULL;

        /*
         * Determine the number of vectors which need interrupt affinities
         * assigned. If the pre/post request exhausts the available vectors
         * then nothing to do here except for invoking the calc_sets()
         * callback so the device driver can adjust to the situation.
         */
        if (nvecs > affd->pre_vectors + affd->post_vectors)
                affvecs = nvecs - affd->pre_vectors - affd->post_vectors;
        else
                affvecs = 0;

        /*
         * Simple invocations do not provide a calc_sets() callback. Install
         * the generic one.
         */
        if (!affd->calc_sets)
                affd->calc_sets = default_calc_sets;

        /* Recalculate the sets */
        affd->calc_sets(affd, affvecs);

        if (WARN_ON_ONCE(affd->nr_sets > IRQ_AFFINITY_MAX_SETS))
                return NULL;

        /* Nothing to assign? */
        if (!affvecs)
                return NULL;

        masks = kcalloc(nvecs, sizeof(*masks), GFP_KERNEL);
        if (!masks)
                return NULL;

        /* Fill out vectors at the beginning that don't need affinity */
        for (curvec = 0; curvec < affd->pre_vectors; curvec++)
                cpumask_copy(&masks[curvec].mask, irq_default_affinity);

        /*
         * Spread on present CPUs starting from affd->pre_vectors. If we
         * have multiple sets, build each sets affinity mask separately.
         */
        for (i = 0, usedvecs = 0; i < affd->nr_sets; i++) {
                unsigned int this_vecs = affd->set_size[i];
                int ret;

                ret = irq_build_affinity_masks(curvec, this_vecs,
                                               curvec, masks);
                if (ret) {
                        kfree(masks);
                        return NULL;
                }
                curvec += this_vecs;
                usedvecs += this_vecs;
        }

        /* Fill out vectors at the end that don't need affinity */
        if (usedvecs >= affvecs)
                curvec = affd->pre_vectors + affvecs;
        else
                curvec = affd->pre_vectors + usedvecs;
        for (; curvec < nvecs; curvec++)
                cpumask_copy(&masks[curvec].mask, irq_default_affinity);

        /* Mark the managed interrupts */
        for (i = affd->pre_vectors; i < nvecs - affd->post_vectors; i++)
                masks[i].is_managed = 1;

        return masks;
}

/**
 * irq_calc_affinity_vectors - Calculate the optimal number of vectors
 * @minvec:     The minimum number of vectors available
 * @maxvec:     The maximum number of vectors available
 * @affd:       Description of the affinity requirements
 */
unsigned int irq_calc_affinity_vectors(unsigned int minvec, unsigned int maxvec,
                                       const struct irq_affinity *affd)
{
        unsigned int resv = affd->pre_vectors + affd->post_vectors;
        unsigned int set_vecs;

        if (resv > minvec)
                return 0;

        if (affd->calc_sets) {
                set_vecs = maxvec - resv;
        } else {
                cpus_read_lock();
                set_vecs = cpumask_weight(cpu_possible_mask);
                cpus_read_unlock();
        }

        return resv + min(set_vecs, maxvec - resv);
}