/* cpumap.c: used for optimizing CPU assignment
 *
 * Copyright (C) 2009 Hong H. Pham <hong.pham@windriver.com>
 */

#include <linux/module.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 = first_cpu(cpu_online_map);

        /* 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:
                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 first_cpu(cpu_online_map);
}

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);
}