async-thread.h

Go to the documentation of this file.

/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#ifndef __BTRFS_ASYNC_THREAD_
#define __BTRFS_ASYNC_THREAD_

struct btrfs_worker_thread;

/*
 * This is similar to a workqueue, but it is meant to spread the operations
 * across all available cpus instead of just the CPU that was used to
 * queue the work.  There is also some batching introduced to try and
 * cut down on context switches.
 *
 * By default threads are added on demand up to 2 * the number of cpus.
 * Changing struct btrfs_workers->max_workers is one way to prevent
 * demand creation of kthreads.
 *
 * the basic model of these worker threads is to embed a btrfs_work
 * structure in your own data struct, and use container_of in a
 * work function to get back to your data struct.
 */
struct btrfs_work {
    /*
     * func should be set to the function you want called
     * your work struct is passed as the only arg
     *
     * ordered_func must be set for work sent to an ordered work queue,
     * and it is called to complete a given work item in the same
     * order they were sent to the queue.
     */
    void (*func)(struct btrfs_work *work);
    void (*ordered_func)(struct btrfs_work *work);
    void (*ordered_free)(struct btrfs_work *work);

    /*
     * flags should be set to zero.  It is used to make sure the
     * struct is only inserted once into the list.
     */
    unsigned long flags;

    /* don't touch these */
    struct btrfs_worker_thread *worker;
    struct list_head list;
    struct list_head order_list;
};

struct btrfs_workers {
    /* current number of running workers */
    int num_workers;

    int num_workers_starting;

    /* max number of workers allowed.  changed by btrfs_start_workers */
    int max_workers;

    /* once a worker has this many requests or fewer, it is idle */
    int idle_thresh;

    /* force completions in the order they were queued */
    int ordered;

    /* more workers required, but in an interrupt handler */
    int atomic_start_pending;

    /*
     * are we allowed to sleep while starting workers or are we required
     * to start them at a later time?  If we can't sleep, this indicates
     * which queue we need to use to schedule thread creation.
     */
    struct btrfs_workers *atomic_worker_start;

    /* list with all the work threads.  The workers on the idle thread
     * may be actively servicing jobs, but they haven't yet hit the
     * idle thresh limit above.
     */
    struct list_head worker_list;
    struct list_head idle_list;

    /*
     * when operating in ordered mode, this maintains the list
     * of work items waiting for completion
     */
    struct list_head order_list;
    struct list_head prio_order_list;

    /* lock for finding the next worker thread to queue on */
    spinlock_t lock;

    /* lock for the ordered lists */
    spinlock_t order_lock;

    /* extra name for this worker, used for current->name */
    char *name;
};

void btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work);
int btrfs_start_workers(struct btrfs_workers *workers);
void btrfs_stop_workers(struct btrfs_workers *workers);
void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max,
            struct btrfs_workers *async_starter);
void btrfs_requeue_work(struct btrfs_work *work);
void btrfs_set_work_high_prio(struct btrfs_work *work);
#endif