source: mainline/kernel/generic/src/sysinfo/stats.c@ a3d87b9

/*
 * Copyright (c) 2010 Stanislav Kozina
 * Copyright (c) 2010 Martin Decky
 * Copyright (c) 2018 Jiri Svoboda
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup kernel_generic
 * @{
 */
/** @file
 */

#include <assert.h>
#include <typedefs.h>
#include <abi/sysinfo.h>
#include <sysinfo/stats.h>
#include <sysinfo/sysinfo.h>
#include <synch/spinlock.h>
#include <synch/mutex.h>
#include <time/clock.h>
#include <mm/frame.h>
#include <proc/task.h>
#include <proc/thread.h>
#include <interrupt.h>
#include <stdbool.h>
#include <str.h>
#include <errno.h>
#include <cpu.h>
#include <arch.h>
#include <stdlib.h>

/** Bits of fixed-point precision for load */
#define LOAD_FIXED_SHIFT  11

/** Uspace load fixed-point precision */
#define LOAD_USPACE_SHIFT  6

/** Kernel load shift */
#define LOAD_KERNEL_SHIFT  (LOAD_FIXED_SHIFT - LOAD_USPACE_SHIFT)

/** 1.0 as fixed-point for load */
#define LOAD_FIXED_1  (1 << LOAD_FIXED_SHIFT)

/** Compute load in 5 second intervals */
#define LOAD_INTERVAL  5

/** IPC connections statistics state */
typedef struct {
        bool counting;
        size_t count;
        size_t i;
        stats_ipcc_t *data;
} ipccs_state_t;

/** Fixed-point representation of
 *
 * 1 / exp(5 sec / 1 min)
 * 1 / exp(5 sec / 5 min)
 * 1 / exp(5 sec / 15 min)
 *
 */
static load_t load_exp[LOAD_STEPS] = { 1884, 2014, 2037 };

/** Running average of the number of ready threads */
static load_t avenrdy[LOAD_STEPS] = { 0, 0, 0 };

/** Load calculation lock */
static mutex_t load_lock;

/** Get statistics of all CPUs
 *
 * @param item    Sysinfo item (unused).
 * @param size    Size of the returned data.
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Data containing several stats_cpu_t structures.
 *         If the return value is not NULL, it should be freed
 *         in the context of the sysinfo request.
 */
static void *get_stats_cpus(struct sysinfo_item *item, size_t *size,
    bool dry_run, void *data)
{
        *size = sizeof(stats_cpu_t) * config.cpu_count;
        if (dry_run)
                return NULL;

        /* Assumption: config.cpu_count is constant */
        stats_cpu_t *stats_cpus = (stats_cpu_t *) malloc(*size);
        if (stats_cpus == NULL) {
                *size = 0;
                return NULL;
        }

        size_t i;
        for (i = 0; i < config.cpu_count; i++) {
                stats_cpus[i].id = cpus[i].id;
                stats_cpus[i].active = cpus[i].active;
                stats_cpus[i].frequency_mhz = cpus[i].frequency_mhz;

                stats_cpus[i].busy_cycles = atomic_time_read(&cpus[i].busy_cycles);
                stats_cpus[i].idle_cycles = atomic_time_read(&cpus[i].idle_cycles);
        }

        return ((void *) stats_cpus);
}

/** Get the size of a virtual address space
 *
 * @param as Address space.
 *
 * @return Size of the mapped virtual address space (bytes).
 *
 */
static size_t get_task_virtmem(as_t *as)
{
        /*
         * We are holding spinlocks here and therefore are not allowed to
         * block. Only attempt to lock the address space and address space
         * area mutexes conditionally. If it is not possible to lock either
         * object, return inexact statistics by skipping the respective object.
         */

        if (mutex_trylock(&as->lock) != EOK)
                return 0;

        size_t pages = 0;

        /* Walk areas in the address space and count pages */
        as_area_t *area = as_area_first(as);
        while (area != NULL) {
                if (mutex_trylock(&area->lock) != EOK)
                        continue;

                pages += area->pages;
                mutex_unlock(&area->lock);
                area = as_area_next(area);
        }

        mutex_unlock(&as->lock);

        return (pages << PAGE_WIDTH);
}

/** Get the resident (used) size of a virtual address space
 *
 * @param as Address space.
 *
 * @return Size of the resident (used) virtual address space (bytes).
 *
 */
static size_t get_task_resmem(as_t *as)
{
        /*
         * We are holding spinlocks here and therefore are not allowed to
         * block. Only attempt to lock the address space and address space
         * area mutexes conditionally. If it is not possible to lock either
         * object, return inexact statistics by skipping the respective object.
         */

        if (mutex_trylock(&as->lock) != EOK)
                return 0;

        size_t pages = 0;

        /* Walk areas in the address space and count pages */
        as_area_t *area = as_area_first(as);
        while (area != NULL) {
                if (mutex_trylock(&area->lock) != EOK)
                        continue;

                pages += area->used_space.pages;
                mutex_unlock(&area->lock);
                area = as_area_next(area);
        }

        mutex_unlock(&as->lock);

        return (pages << PAGE_WIDTH);
}

/** Produce task statistics
 *
 * Summarize task information into task statistics.
 *
 * @param task       Task.
 * @param stats_task Task statistics.
 *
 */
static void produce_stats_task(task_t *task, stats_task_t *stats_task)
{
        assert(interrupts_disabled());
        assert(irq_spinlock_locked(&task->lock));

        stats_task->task_id = task->taskid;
        str_cpy(stats_task->name, TASK_NAME_BUFLEN, task->name);
        stats_task->virtmem = get_task_virtmem(task->as);
        stats_task->resmem = get_task_resmem(task->as);
        stats_task->threads = atomic_load(&task->refcount);
        task_get_accounting(task, &(stats_task->ucycles),
            &(stats_task->kcycles));
        stats_task->ipc_info = task->ipc_info;
}

/** Get task statistics
 *
 * @param item    Sysinfo item (unused).
 * @param size    Size of the returned data.
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Data containing several stats_task_t structures.
 *         If the return value is not NULL, it should be freed
 *         in the context of the sysinfo request.
 */
static void *get_stats_tasks(struct sysinfo_item *item, size_t *size,
    bool dry_run, void *data)
{
        /* Messing with task structures, avoid deadlock */
        irq_spinlock_lock(&tasks_lock, true);

        /* Count the tasks */
        size_t count = task_count();

        if (count == 0) {
                /* No tasks found (strange) */
                irq_spinlock_unlock(&tasks_lock, true);
                *size = 0;
                return NULL;
        }

        *size = sizeof(stats_task_t) * count;
        if (dry_run) {
                irq_spinlock_unlock(&tasks_lock, true);
                return NULL;
        }

        stats_task_t *stats_tasks = (stats_task_t *) malloc(*size);
        if (stats_tasks == NULL) {
                /* No free space for allocation */
                irq_spinlock_unlock(&tasks_lock, true);
                *size = 0;
                return NULL;
        }

        /* Gather the statistics for each task */
        size_t i = 0;
        task_t *task = task_first();
        while (task != NULL) {
                /* Interrupts are already disabled */
                irq_spinlock_lock(&(task->lock), false);

                /* Record the statistics and increment the index */
                produce_stats_task(task, &stats_tasks[i]);
                i++;

                irq_spinlock_unlock(&(task->lock), false);
                task = task_next(task);
        }

        irq_spinlock_unlock(&tasks_lock, true);

        return ((void *) stats_tasks);
}

/** Produce thread statistics
 *
 * Summarize thread information into thread statistics.
 *
 * @param thread       Thread.
 * @param stats_thread Thread statistics.
 *
 */
static void produce_stats_thread(thread_t *thread, stats_thread_t *stats_thread)
{
        assert(interrupts_disabled());

        stats_thread->thread_id = thread->tid;
        stats_thread->task_id = thread->task->taskid;
        stats_thread->state = atomic_get_unordered(&thread->state);
        stats_thread->priority = atomic_get_unordered(&thread->priority);
        stats_thread->ucycles = atomic_time_read(&thread->ucycles);
        stats_thread->kcycles = atomic_time_read(&thread->kcycles);

        cpu_t *cpu = atomic_get_unordered(&thread->cpu);

        if (cpu != NULL) {
                stats_thread->on_cpu = true;
                stats_thread->cpu = cpu->id;
        } else
                stats_thread->on_cpu = false;
}

/** Get thread statistics
 *
 * @param item    Sysinfo item (unused).
 * @param size    Size of the returned data.
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Data containing several stats_task_t structures.
 *         If the return value is not NULL, it should be freed
 *         in the context of the sysinfo request.
 */
static void *get_stats_threads(struct sysinfo_item *item, size_t *size,
    bool dry_run, void *data)
{
        /* Messing with threads structures */
        irq_spinlock_lock(&threads_lock, true);

        /* Count the threads */
        size_t count = thread_count();

        if (count == 0) {
                /* No threads found (strange) */
                irq_spinlock_unlock(&threads_lock, true);
                *size = 0;
                return NULL;
        }

        *size = sizeof(stats_thread_t) * count;
        if (dry_run) {
                irq_spinlock_unlock(&threads_lock, true);
                return NULL;
        }

        stats_thread_t *stats_threads = (stats_thread_t *) malloc(*size);
        if (stats_threads == NULL) {
                /* No free space for allocation */
                irq_spinlock_unlock(&threads_lock, true);
                *size = 0;
                return NULL;
        }

        /* Walk tha thread tree again to gather the statistics */
        size_t i = 0;

        thread_t *thread = thread_first();
        while (thread != NULL) {
                /* Interrupts are already disabled */
                irq_spinlock_lock(&thread->lock, false);

                /* Record the statistics and increment the index */
                produce_stats_thread(thread, &stats_threads[i]);
                i++;

                irq_spinlock_unlock(&thread->lock, false);

                thread = thread_next(thread);
        }

        irq_spinlock_unlock(&threads_lock, true);

        return ((void *) stats_threads);
}

/** Produce IPC connection statistics
 *
 * Summarize IPC connection information into IPC connection statistics.
 *
 * @param cap Phone capability.
 * @param arg State variable.
 *
 */
static bool produce_stats_ipcc_cb(cap_t *cap, void *arg)
{
        phone_t *phone = cap->kobject->phone;
        ipccs_state_t *state = (ipccs_state_t *) arg;

        if (state->counting) {
                /*
                 * Simply update the number of entries
                 * in case we are in the counting mode.
                 */

                state->count++;
                return true;
        }

        /* We are in the gathering mode */

        if ((state->data == NULL) || (state->i >= state->count)) {
                /*
                 * Do nothing if we have no buffer
                 * to store the data to (meaning we are
                 * in a dry run) or the buffer is already
                 * full.
                 */

                return true;
        }

        mutex_lock(&phone->lock);

        if (phone->state == IPC_PHONE_CONNECTED) {
                state->data[state->i].caller = phone->caller->taskid;
                state->data[state->i].callee = phone->callee->task->taskid;
                state->i++;
        }

        mutex_unlock(&phone->lock);

        return true;
}

/** Get IPC connections statistics
 *
 * @param item    Sysinfo item (unused).
 * @param size    Size of the returned data.
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Data containing several stats_ipccs_t structures.
 *         If the return value is not NULL, it should be freed
 *         in the context of the sysinfo request.
 *
 */
static void *get_stats_ipccs(struct sysinfo_item *item, size_t *size,
    bool dry_run, void *data)
{
        /* Messing with tasks structures, avoid deadlock */
        irq_spinlock_lock(&tasks_lock, true);

        ipccs_state_t state = {
                .counting = true,
                .count = 0,
                .i = 0,
                .data = NULL
        };

        /* Compute the number of IPC connections */
        task_t *task = task_first();
        while (task != NULL) {
                task_hold(task);
                irq_spinlock_unlock(&tasks_lock, true);

                caps_apply_to_kobject_type(task, KOBJECT_TYPE_PHONE,
                    produce_stats_ipcc_cb, &state);

                irq_spinlock_lock(&tasks_lock, true);

                task = task_next(task);
        }

        state.counting = false;
        *size = sizeof(stats_ipcc_t) * state.count;

        if (!dry_run)
                state.data = (stats_ipcc_t *) malloc(*size);

        /* Gather the statistics for each task */
        task = task_first();
        while (task != NULL) {
                /* We already hold a reference to the task */
                irq_spinlock_unlock(&tasks_lock, true);

                caps_apply_to_kobject_type(task, KOBJECT_TYPE_PHONE,
                    produce_stats_ipcc_cb, &state);

                irq_spinlock_lock(&tasks_lock, true);

                task_t *prev_task = task;
                task = task_next(prev_task);
                task_release(prev_task);
        }

        irq_spinlock_unlock(&tasks_lock, true);

        return ((void *) state.data);
}

/** Get a single task statistics
 *
 * Get statistics of a given task. The task ID is passed
 * as a string (current limitation of the sysinfo interface,
 * but it is still reasonable for the given purpose).
 *
 * @param name    Task ID (string-encoded number).
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Sysinfo return holder. The type of the returned
 *         data is either SYSINFO_VAL_UNDEFINED (unknown
 *         task ID or memory allocation error) or
 *         SYSINFO_VAL_FUNCTION_DATA (in that case the
 *         generated data should be freed within the
 *         sysinfo request context).
 *
 */
static sysinfo_return_t get_stats_task(const char *name, bool dry_run,
    void *data)
{
        /* Initially no return value */
        sysinfo_return_t ret;
        ret.tag = SYSINFO_VAL_UNDEFINED;

        /* Parse the task ID */
        task_id_t task_id;
        if (str_uint64_t(name, NULL, 0, true, &task_id) != EOK)
                return ret;

        /* Messing with task structures, avoid deadlock */
        irq_spinlock_lock(&tasks_lock, true);

        task_t *task = task_find_by_id(task_id);
        if (task == NULL) {
                /* No task with this ID */
                irq_spinlock_unlock(&tasks_lock, true);
                return ret;
        }

        if (dry_run) {
                ret.tag = SYSINFO_VAL_FUNCTION_DATA;
                ret.data.data = NULL;
                ret.data.size = sizeof(stats_task_t);

                irq_spinlock_unlock(&tasks_lock, true);
        } else {
                /* Allocate stats_task_t structure */
                stats_task_t *stats_task =
                    (stats_task_t *) malloc(sizeof(stats_task_t));
                if (stats_task == NULL) {
                        irq_spinlock_unlock(&tasks_lock, true);
                        return ret;
                }

                /* Correct return value */
                ret.tag = SYSINFO_VAL_FUNCTION_DATA;
                ret.data.data = (void *) stats_task;
                ret.data.size = sizeof(stats_task_t);

                /* Hand-over-hand locking */
                irq_spinlock_exchange(&tasks_lock, &task->lock);

                produce_stats_task(task, stats_task);

                irq_spinlock_unlock(&task->lock, true);
        }

        return ret;
}

/** Get thread statistics
 *
 * Get statistics of a given thread. The thread ID is passed
 * as a string (current limitation of the sysinfo interface,
 * but it is still reasonable for the given purpose).
 *
 * @param name    Thread ID (string-encoded number).
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Sysinfo return holder. The type of the returned
 *         data is either SYSINFO_VAL_UNDEFINED (unknown
 *         thread ID or memory allocation error) or
 *         SYSINFO_VAL_FUNCTION_DATA (in that case the
 *         generated data should be freed within the
 *         sysinfo request context).
 *
 */
static sysinfo_return_t get_stats_thread(const char *name, bool dry_run,
    void *data)
{
        /* Initially no return value */
        sysinfo_return_t ret;
        ret.tag = SYSINFO_VAL_UNDEFINED;

        /* Parse the thread ID */
        thread_id_t thread_id;
        if (str_uint64_t(name, NULL, 0, true, &thread_id) != EOK)
                return ret;

        /* Messing with threads structures */
        irq_spinlock_lock(&threads_lock, true);

        thread_t *thread = thread_find_by_id(thread_id);
        if (thread == NULL) {
                /* No thread with this ID */
                irq_spinlock_unlock(&threads_lock, true);
                return ret;
        }

        if (dry_run) {
                ret.tag = SYSINFO_VAL_FUNCTION_DATA;
                ret.data.data = NULL;
                ret.data.size = sizeof(stats_thread_t);

                irq_spinlock_unlock(&threads_lock, true);
        } else {
                /* Allocate stats_thread_t structure */
                stats_thread_t *stats_thread =
                    (stats_thread_t *) malloc(sizeof(stats_thread_t));
                if (stats_thread == NULL) {
                        irq_spinlock_unlock(&threads_lock, true);
                        return ret;
                }

                /* Correct return value */
                ret.tag = SYSINFO_VAL_FUNCTION_DATA;
                ret.data.data = (void *) stats_thread;
                ret.data.size = sizeof(stats_thread_t);

                /*
                 * Replaced hand-over-hand locking with regular nested sections
                 * to avoid weak reference leak issues.
                 */
                irq_spinlock_lock(&thread->lock, false);
                produce_stats_thread(thread, stats_thread);
                irq_spinlock_unlock(&thread->lock, false);

                irq_spinlock_unlock(&threads_lock, true);
        }

        return ret;
}

/** Get exceptions statistics
 *
 * @param item    Sysinfo item (unused).
 * @param size    Size of the returned data.
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Data containing several stats_exc_t structures.
 *         If the return value is not NULL, it should be freed
 *         in the context of the sysinfo request.
 */
static void *get_stats_exceptions(struct sysinfo_item *item, size_t *size,
    bool dry_run, void *data)
{
        *size = sizeof(stats_exc_t) * IVT_ITEMS;

        if ((dry_run) || (IVT_ITEMS == 0))
                return NULL;

        stats_exc_t *stats_exceptions =
            (stats_exc_t *) malloc(*size);
        if (stats_exceptions == NULL) {
                /* No free space for allocation */
                *size = 0;
                return NULL;
        }

#if (IVT_ITEMS > 0)
        /* Messing with exception table, avoid deadlock */
        irq_spinlock_lock(&exctbl_lock, true);

        unsigned int i;
        for (i = 0; i < IVT_ITEMS; i++) {
                stats_exceptions[i].id = i + IVT_FIRST;
                str_cpy(stats_exceptions[i].desc, EXC_NAME_BUFLEN, exc_table[i].name);
                stats_exceptions[i].hot = exc_table[i].hot;
                stats_exceptions[i].cycles = exc_table[i].cycles;
                stats_exceptions[i].count = exc_table[i].count;
        }

        irq_spinlock_unlock(&exctbl_lock, true);
#endif

        return ((void *) stats_exceptions);
}

/** Get exception statistics
 *
 * Get statistics of a given exception. The exception number
 * is passed as a string (current limitation of the sysinfo
 * interface, but it is still reasonable for the given purpose).
 *
 * @param name    Exception number (string-encoded number).
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Sysinfo return holder. The type of the returned
 *         data is either SYSINFO_VAL_UNDEFINED (unknown
 *         exception number or memory allocation error) or
 *         SYSINFO_VAL_FUNCTION_DATA (in that case the
 *         generated data should be freed within the
 *         sysinfo request context).
 *
 */
static sysinfo_return_t get_stats_exception(const char *name, bool dry_run,
    void *data)
{
        /* Initially no return value */
        sysinfo_return_t ret;
        ret.tag = SYSINFO_VAL_UNDEFINED;

        /* Parse the exception number */
        uint64_t excn;
        if (str_uint64_t(name, NULL, 0, true, &excn) != EOK)
                return ret;

#if (IVT_FIRST > 0)
        if (excn < IVT_FIRST)
                return ret;
#endif

#if (IVT_ITEMS + IVT_FIRST == 0)
        return ret;
#else
        if (excn >= IVT_ITEMS + IVT_FIRST)
                return ret;
#endif

        if (dry_run) {
                ret.tag = SYSINFO_VAL_FUNCTION_DATA;
                ret.data.data = NULL;
                ret.data.size = sizeof(stats_thread_t);
        } else {
                /* Update excn index for accessing exc_table */
                excn -= IVT_FIRST;

                /* Allocate stats_exc_t structure */
                stats_exc_t *stats_exception =
                    (stats_exc_t *) malloc(sizeof(stats_exc_t));
                if (stats_exception == NULL)
                        return ret;

                /* Messing with exception table, avoid deadlock */
                irq_spinlock_lock(&exctbl_lock, true);

                /* Correct return value */
                ret.tag = SYSINFO_VAL_FUNCTION_DATA;
                ret.data.data = (void *) stats_exception;
                ret.data.size = sizeof(stats_exc_t);

                stats_exception->id = excn;
                str_cpy(stats_exception->desc, EXC_NAME_BUFLEN, exc_table[excn].name);
                stats_exception->hot = exc_table[excn].hot;
                stats_exception->cycles = exc_table[excn].cycles;
                stats_exception->count = exc_table[excn].count;

                irq_spinlock_unlock(&exctbl_lock, true);
        }

        return ret;
}

/** Get physical memory statistics
 *
 * @param item    Sysinfo item (unused).
 * @param size    Size of the returned data.
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Data containing stats_physmem_t.
 *         If the return value is not NULL, it should be freed
 *         in the context of the sysinfo request.
 */
static void *get_stats_physmem(struct sysinfo_item *item, size_t *size,
    bool dry_run, void *data)
{
        *size = sizeof(stats_physmem_t);
        if (dry_run)
                return NULL;

        stats_physmem_t *stats_physmem =
            (stats_physmem_t *) malloc(*size);
        if (stats_physmem == NULL) {
                *size = 0;
                return NULL;
        }

        zones_stats(&(stats_physmem->total), &(stats_physmem->unavail),
            &(stats_physmem->used), &(stats_physmem->free));

        return ((void *) stats_physmem);
}

/** Get system load
 *
 * @param item    Sysinfo item (unused).
 * @param size    Size of the returned data.
 * @param dry_run Do not get the data, just calculate the size.
 * @param data    Unused.
 *
 * @return Data several load_t values.
 *         If the return value is not NULL, it should be freed
 *         in the context of the sysinfo request.
 */
static void *get_stats_load(struct sysinfo_item *item, size_t *size,
    bool dry_run, void *data)
{
        *size = sizeof(load_t) * LOAD_STEPS;
        if (dry_run)
                return NULL;

        load_t *stats_load = (load_t *) malloc(*size);
        if (stats_load == NULL) {
                *size = 0;
                return NULL;
        }

        /* To always get consistent values acquire the mutex */
        mutex_lock(&load_lock);

        unsigned int i;
        for (i = 0; i < LOAD_STEPS; i++)
                stats_load[i] = avenrdy[i] << LOAD_KERNEL_SHIFT;

        mutex_unlock(&load_lock);

        return ((void *) stats_load);
}

/** Calculate load
 *
 */
static inline load_t load_calc(load_t load, load_t exp, size_t ready)
{
        load *= exp;
        load += (ready << LOAD_FIXED_SHIFT) * (LOAD_FIXED_1 - exp);

        return (load >> LOAD_FIXED_SHIFT);
}

/** Load computation thread.
 *
 * Compute system load every few seconds.
 *
 * @param arg Unused.
 *
 */
void kload(void *arg)
{
        while (true) {
                size_t ready = atomic_load(&nrdy);

                /* Mutually exclude with get_stats_load() */
                mutex_lock(&load_lock);

                unsigned int i;
                for (i = 0; i < LOAD_STEPS; i++)
                        avenrdy[i] = load_calc(avenrdy[i], load_exp[i], ready);

                mutex_unlock(&load_lock);

                thread_sleep(LOAD_INTERVAL);
        }
}

/** Register sysinfo statistical items
 *
 */
void stats_init(void)
{
        mutex_initialize(&load_lock, MUTEX_PASSIVE);

        sysinfo_set_item_gen_data("system.cpus", NULL, get_stats_cpus, NULL);
        sysinfo_set_item_gen_data("system.physmem", NULL, get_stats_physmem, NULL);
        sysinfo_set_item_gen_data("system.load", NULL, get_stats_load, NULL);
        sysinfo_set_item_gen_data("system.tasks", NULL, get_stats_tasks, NULL);
        sysinfo_set_item_gen_data("system.threads", NULL, get_stats_threads, NULL);
        sysinfo_set_item_gen_data("system.ipccs", NULL, get_stats_ipccs, NULL);
        sysinfo_set_item_gen_data("system.exceptions", NULL, get_stats_exceptions, NULL);
        sysinfo_set_subtree_fn("system.tasks", NULL, get_stats_task, NULL);
        sysinfo_set_subtree_fn("system.threads", NULL, get_stats_thread, NULL);
        sysinfo_set_subtree_fn("system.exceptions", NULL, get_stats_exception, NULL);
}

/** @}
 */