cpumap.c

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/* cpumap.c: used for optimizing CPU assignment
 *
 * Copyright (C) 2009 Hong H. Pham <[email protected]>
 */

#include <linux/export.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/cpumask.h>
#include <linux/spinlock.h>
#include <asm/cpudata.h>
#include "cpumap.h"


enum {
    CPUINFO_LVL_ROOT = 0,
    CPUINFO_LVL_NODE,
    CPUINFO_LVL_CORE,
    CPUINFO_LVL_PROC,
    CPUINFO_LVL_MAX,
};

enum {
    ROVER_NO_OP              = 0,
    /* Increment rover every time level is visited */
    ROVER_INC_ON_VISIT       = 1 << 0,
    /* Increment parent's rover every time rover wraps around */
    ROVER_INC_PARENT_ON_LOOP = 1 << 1,
};

struct cpuinfo_node {
    int id;
    int level;
    int num_cpus;    /* Number of CPUs in this hierarchy */
    int parent_index;
    int child_start; /* Array index of the first child node */
    int child_end;   /* Array index of the last child node */
    int rover;       /* Child node iterator */
};

struct cpuinfo_level {
    int start_index; /* Index of first node of a level in a cpuinfo tree */
    int end_index;   /* Index of last node of a level in a cpuinfo tree */
    int num_nodes;   /* Number of nodes in a level in a cpuinfo tree */
};

struct cpuinfo_tree {
    int total_nodes;

    /* Offsets into nodes[] for each level of the tree */
    struct cpuinfo_level level[CPUINFO_LVL_MAX];
    struct cpuinfo_node  nodes[0];
};


static struct cpuinfo_tree *cpuinfo_tree;

static u16 cpu_distribution_map[NR_CPUS];
static DEFINE_SPINLOCK(cpu_map_lock);


/* Niagara optimized cpuinfo tree traversal. */
static const int niagara_iterate_method[] = {
    [CPUINFO_LVL_ROOT] = ROVER_NO_OP,

    /* Strands (or virtual CPUs) within a core may not run concurrently
     * on the Niagara, as instruction pipeline(s) are shared.  Distribute
     * work to strands in different cores first for better concurrency.
     * Go to next NUMA node when all cores are used.
     */
    [CPUINFO_LVL_NODE] = ROVER_INC_ON_VISIT|ROVER_INC_PARENT_ON_LOOP,

    /* Strands are grouped together by proc_id in cpuinfo_sparc, i.e.
     * a proc_id represents an instruction pipeline.  Distribute work to
     * strands in different proc_id groups if the core has multiple
     * instruction pipelines (e.g. the Niagara 2/2+ has two).
     */
    [CPUINFO_LVL_CORE] = ROVER_INC_ON_VISIT,

    /* Pick the next strand in the proc_id group. */
    [CPUINFO_LVL_PROC] = ROVER_INC_ON_VISIT,
};

/* Generic cpuinfo tree traversal.  Distribute work round robin across NUMA
 * nodes.
 */
static const int generic_iterate_method[] = {
    [CPUINFO_LVL_ROOT] = ROVER_INC_ON_VISIT,
    [CPUINFO_LVL_NODE] = ROVER_NO_OP,
    [CPUINFO_LVL_CORE] = ROVER_INC_PARENT_ON_LOOP,
    [CPUINFO_LVL_PROC] = ROVER_INC_ON_VISIT|ROVER_INC_PARENT_ON_LOOP,
};


static int cpuinfo_id(int cpu, int level)
{
    int id;

    switch (level) {
    case CPUINFO_LVL_ROOT:
        id = 0;
        break;
    case CPUINFO_LVL_NODE:
        id = cpu_to_node(cpu);
        break;
    case CPUINFO_LVL_CORE:
        id = cpu_data(cpu).core_id;
        break;
    case CPUINFO_LVL_PROC:
        id = cpu_data(cpu).proc_id;
        break;
    default:
        id = -EINVAL;
    }
    return id;
}

/*
 * Enumerate the CPU information in __cpu_data to determine the start index,
 * end index, and number of nodes for each level in the cpuinfo tree.  The
 * total number of cpuinfo nodes required to build the tree is returned.
 */
static int enumerate_cpuinfo_nodes(struct cpuinfo_level *tree_level)
{
    int prev_id[CPUINFO_LVL_MAX];
    int i, n, num_nodes;

    for (i = CPUINFO_LVL_ROOT; i < CPUINFO_LVL_MAX; i++) {
        struct cpuinfo_level *lv = &tree_level[i];

        prev_id[i] = -1;
        lv->start_index = lv->end_index = lv->num_nodes = 0;
    }

    num_nodes = 1; /* Include the root node */

    for (i = 0; i < num_possible_cpus(); i++) {
        if (!cpu_online(i))
            continue;

        n = cpuinfo_id(i, CPUINFO_LVL_NODE);
        if (n > prev_id[CPUINFO_LVL_NODE]) {
            tree_level[CPUINFO_LVL_NODE].num_nodes++;
            prev_id[CPUINFO_LVL_NODE] = n;
            num_nodes++;
        }
        n = cpuinfo_id(i, CPUINFO_LVL_CORE);
        if (n > prev_id[CPUINFO_LVL_CORE]) {
            tree_level[CPUINFO_LVL_CORE].num_nodes++;
            prev_id[CPUINFO_LVL_CORE] = n;
            num_nodes++;
        }
        n = cpuinfo_id(i, CPUINFO_LVL_PROC);
        if (n > prev_id[CPUINFO_LVL_PROC]) {
            tree_level[CPUINFO_LVL_PROC].num_nodes++;
            prev_id[CPUINFO_LVL_PROC] = n;
            num_nodes++;
        }
    }

    tree_level[CPUINFO_LVL_ROOT].num_nodes = 1;

    n = tree_level[CPUINFO_LVL_NODE].num_nodes;
    tree_level[CPUINFO_LVL_NODE].start_index = 1;
    tree_level[CPUINFO_LVL_NODE].end_index   = n;

    n++;
    tree_level[CPUINFO_LVL_CORE].start_index = n;
    n += tree_level[CPUINFO_LVL_CORE].num_nodes;
    tree_level[CPUINFO_LVL_CORE].end_index   = n - 1;

    tree_level[CPUINFO_LVL_PROC].start_index = n;
    n += tree_level[CPUINFO_LVL_PROC].num_nodes;
    tree_level[CPUINFO_LVL_PROC].end_index   = n - 1;

    return num_nodes;
}

/* Build a tree representation of the CPU hierarchy using the per CPU
 * information in __cpu_data.  Entries in __cpu_data[0..NR_CPUS] are
 * assumed to be sorted in ascending order based on node, core_id, and
 * proc_id (in order of significance).
 */
static struct cpuinfo_tree *build_cpuinfo_tree(void)
{
    struct cpuinfo_tree *new_tree;
    struct cpuinfo_node *node;
    struct cpuinfo_level tmp_level[CPUINFO_LVL_MAX];
    int num_cpus[CPUINFO_LVL_MAX];
    int level_rover[CPUINFO_LVL_MAX];
    int prev_id[CPUINFO_LVL_MAX];
    int n, id, cpu, prev_cpu, last_cpu, level;

    n = enumerate_cpuinfo_nodes(tmp_level);

    new_tree = kzalloc(sizeof(struct cpuinfo_tree) +
                       (sizeof(struct cpuinfo_node) * n), GFP_ATOMIC);
    if (!new_tree)
        return NULL;

    new_tree->total_nodes = n;
    memcpy(&new_tree->level, tmp_level, sizeof(tmp_level));

    prev_cpu = cpu = cpumask_first(cpu_online_mask);

    /* Initialize all levels in the tree with the first CPU */
    for (level = CPUINFO_LVL_PROC; level >= CPUINFO_LVL_ROOT; level--) {
        n = new_tree->level[level].start_index;

        level_rover[level] = n;
        node = &new_tree->nodes[n];

        id = cpuinfo_id(cpu, level);
        if (unlikely(id < 0)) {
            kfree(new_tree);
            return NULL;
        }
        node->id = id;
        node->level = level;
        node->num_cpus = 1;

        node->parent_index = (level > CPUINFO_LVL_ROOT)
            ? new_tree->level[level - 1].start_index : -1;

        node->child_start = node->child_end = node->rover =
            (level == CPUINFO_LVL_PROC)
            ? cpu : new_tree->level[level + 1].start_index;

        prev_id[level] = node->id;
        num_cpus[level] = 1;
    }

    for (last_cpu = (num_possible_cpus() - 1); last_cpu >= 0; last_cpu--) {
        if (cpu_online(last_cpu))
            break;
    }

    while (++cpu <= last_cpu) {
        if (!cpu_online(cpu))
            continue;

        for (level = CPUINFO_LVL_PROC; level >= CPUINFO_LVL_ROOT;
             level--) {
            id = cpuinfo_id(cpu, level);
            if (unlikely(id < 0)) {
                kfree(new_tree);
                return NULL;
            }

            if ((id != prev_id[level]) || (cpu == last_cpu)) {
                prev_id[level] = id;
                node = &new_tree->nodes[level_rover[level]];
                node->num_cpus = num_cpus[level];
                num_cpus[level] = 1;

                if (cpu == last_cpu)
                    node->num_cpus++;

                /* Connect tree node to parent */
                if (level == CPUINFO_LVL_ROOT)
                    node->parent_index = -1;
                else
                    node->parent_index =
                        level_rover[level - 1];

                if (level == CPUINFO_LVL_PROC) {
                    node->child_end =
                        (cpu == last_cpu) ? cpu : prev_cpu;
                } else {
                    node->child_end =
                        level_rover[level + 1] - 1;
                }

                /* Initialize the next node in the same level */
                n = ++level_rover[level];
                if (n <= new_tree->level[level].end_index) {
                    node = &new_tree->nodes[n];
                    node->id = id;
                    node->level = level;

                    /* Connect node to child */
                    node->child_start = node->child_end =
                    node->rover =
                        (level == CPUINFO_LVL_PROC)
                        ? cpu : level_rover[level + 1];
                }
            } else
                num_cpus[level]++;
        }
        prev_cpu = cpu;
    }

    return new_tree;
}

static void increment_rover(struct cpuinfo_tree *t, int node_index,
                            int root_index, const int *rover_inc_table)
{
    struct cpuinfo_node *node = &t->nodes[node_index];
    int top_level, level;

    top_level = t->nodes[root_index].level;
    for (level = node->level; level >= top_level; level--) {
        node->rover++;
        if (node->rover <= node->child_end)
            return;

        node->rover = node->child_start;
        /* If parent's rover does not need to be adjusted, stop here. */
        if ((level == top_level) ||
            !(rover_inc_table[level] & ROVER_INC_PARENT_ON_LOOP))
            return;

        node = &t->nodes[node->parent_index];
    }
}

static int iterate_cpu(struct cpuinfo_tree *t, unsigned int root_index)
{
    const int *rover_inc_table;
    int level, new_index, index = root_index;

    switch (sun4v_chip_type) {
    case SUN4V_CHIP_NIAGARA1:
    case SUN4V_CHIP_NIAGARA2:
    case SUN4V_CHIP_NIAGARA3:
    case SUN4V_CHIP_NIAGARA4:
    case SUN4V_CHIP_NIAGARA5:
        rover_inc_table = niagara_iterate_method;
        break;
    default:
        rover_inc_table = generic_iterate_method;
    }

    for (level = t->nodes[root_index].level; level < CPUINFO_LVL_MAX;
         level++) {
        new_index = t->nodes[index].rover;
        if (rover_inc_table[level] & ROVER_INC_ON_VISIT)
            increment_rover(t, index, root_index, rover_inc_table);

        index = new_index;
    }
    return index;
}

static void _cpu_map_rebuild(void)
{
    int i;

    if (cpuinfo_tree) {
        kfree(cpuinfo_tree);
        cpuinfo_tree = NULL;
    }

    cpuinfo_tree = build_cpuinfo_tree();
    if (!cpuinfo_tree)
        return;

    /* Build CPU distribution map that spans all online CPUs.  No need
     * to check if the CPU is online, as that is done when the cpuinfo
     * tree is being built.
     */
    for (i = 0; i < cpuinfo_tree->nodes[0].num_cpus; i++)
        cpu_distribution_map[i] = iterate_cpu(cpuinfo_tree, 0);
}

/* Fallback if the cpuinfo tree could not be built.  CPU mapping is linear
 * round robin.
 */
static int simple_map_to_cpu(unsigned int index)
{
    int i, end, cpu_rover;

    cpu_rover = 0;
    end = index % num_online_cpus();
    for (i = 0; i < num_possible_cpus(); i++) {
        if (cpu_online(cpu_rover)) {
            if (cpu_rover >= end)
                return cpu_rover;

            cpu_rover++;
        }
    }

    /* Impossible, since num_online_cpus() <= num_possible_cpus() */
    return cpumask_first(cpu_online_mask);
}

static int _map_to_cpu(unsigned int index)
{
    struct cpuinfo_node *root_node;

    if (unlikely(!cpuinfo_tree)) {
        _cpu_map_rebuild();
        if (!cpuinfo_tree)
            return simple_map_to_cpu(index);
    }

    root_node = &cpuinfo_tree->nodes[0];
#ifdef CONFIG_HOTPLUG_CPU
    if (unlikely(root_node->num_cpus != num_online_cpus())) {
        _cpu_map_rebuild();
        if (!cpuinfo_tree)
            return simple_map_to_cpu(index);
    }
#endif
    return cpu_distribution_map[index % root_node->num_cpus];
}

int map_to_cpu(unsigned int index)
{
    int mapped_cpu;
    unsigned long flag;

    spin_lock_irqsave(&cpu_map_lock, flag);
    mapped_cpu = _map_to_cpu(index);

#ifdef CONFIG_HOTPLUG_CPU
    while (unlikely(!cpu_online(mapped_cpu)))
        mapped_cpu = _map_to_cpu(index);
#endif
    spin_unlock_irqrestore(&cpu_map_lock, flag);
    return mapped_cpu;
}
EXPORT_SYMBOL(map_to_cpu);

void cpu_map_rebuild(void)
{
    unsigned long flag;

    spin_lock_irqsave(&cpu_map_lock, flag);
    _cpu_map_rebuild();
    spin_unlock_irqrestore(&cpu_map_lock, flag);
}