diff options
Diffstat (limited to 'fs/btrfs/async-thread.c')
| -rw-r--r-- | fs/btrfs/async-thread.c | 419 |
1 files changed, 419 insertions, 0 deletions
diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c new file mode 100644 index 00000000000..8e2fec05dbe --- /dev/null +++ b/fs/btrfs/async-thread.c @@ -0,0 +1,419 @@ +/* + * 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. + */ + +#include <linux/version.h> +#include <linux/kthread.h> +#include <linux/list.h> +#include <linux/spinlock.h> +# include <linux/freezer.h> +#include "async-thread.h" + +#define WORK_QUEUED_BIT 0 +#define WORK_DONE_BIT 1 +#define WORK_ORDER_DONE_BIT 2 + +/* + * container for the kthread task pointer and the list of pending work + * One of these is allocated per thread. + */ +struct btrfs_worker_thread { + /* pool we belong to */ + struct btrfs_workers *workers; + + /* list of struct btrfs_work that are waiting for service */ + struct list_head pending; + + /* list of worker threads from struct btrfs_workers */ + struct list_head worker_list; + + /* kthread */ + struct task_struct *task; + + /* number of things on the pending list */ + atomic_t num_pending; + + unsigned long sequence; + + /* protects the pending list. */ + spinlock_t lock; + + /* set to non-zero when this thread is already awake and kicking */ + int working; + + /* are we currently idle */ + int idle; +}; + +/* + * helper function to move a thread onto the idle list after it + * has finished some requests. + */ +static void check_idle_worker(struct btrfs_worker_thread *worker) +{ + if (!worker->idle && atomic_read(&worker->num_pending) < + worker->workers->idle_thresh / 2) { + unsigned long flags; + spin_lock_irqsave(&worker->workers->lock, flags); + worker->idle = 1; + list_move(&worker->worker_list, &worker->workers->idle_list); + spin_unlock_irqrestore(&worker->workers->lock, flags); + } +} + +/* + * helper function to move a thread off the idle list after new + * pending work is added. + */ +static void check_busy_worker(struct btrfs_worker_thread *worker) +{ + if (worker->idle && atomic_read(&worker->num_pending) >= + worker->workers->idle_thresh) { + unsigned long flags; + spin_lock_irqsave(&worker->workers->lock, flags); + worker->idle = 0; + list_move_tail(&worker->worker_list, + &worker->workers->worker_list); + spin_unlock_irqrestore(&worker->workers->lock, flags); + } +} + +static noinline int run_ordered_completions(struct btrfs_workers *workers, + struct btrfs_work *work) +{ + unsigned long flags; + + if (!workers->ordered) + return 0; + + set_bit(WORK_DONE_BIT, &work->flags); + + spin_lock_irqsave(&workers->lock, flags); + + while (!list_empty(&workers->order_list)) { + work = list_entry(workers->order_list.next, + struct btrfs_work, order_list); + + if (!test_bit(WORK_DONE_BIT, &work->flags)) + break; + + /* we are going to call the ordered done function, but + * we leave the work item on the list as a barrier so + * that later work items that are done don't have their + * functions called before this one returns + */ + if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags)) + break; + + spin_unlock_irqrestore(&workers->lock, flags); + + work->ordered_func(work); + + /* now take the lock again and call the freeing code */ + spin_lock_irqsave(&workers->lock, flags); + list_del(&work->order_list); + work->ordered_free(work); + } + + spin_unlock_irqrestore(&workers->lock, flags); + return 0; +} + +/* + * main loop for servicing work items + */ +static int worker_loop(void *arg) +{ + struct btrfs_worker_thread *worker = arg; + struct list_head *cur; + struct btrfs_work *work; + do { + spin_lock_irq(&worker->lock); + while (!list_empty(&worker->pending)) { + cur = worker->pending.next; + work = list_entry(cur, struct btrfs_work, list); + list_del(&work->list); + clear_bit(WORK_QUEUED_BIT, &work->flags); + + work->worker = worker; + spin_unlock_irq(&worker->lock); + + work->func(work); + + atomic_dec(&worker->num_pending); + /* + * unless this is an ordered work queue, + * 'work' was probably freed by func above. + */ + run_ordered_completions(worker->workers, work); + + spin_lock_irq(&worker->lock); + check_idle_worker(worker); + + } + worker->working = 0; + if (freezing(current)) { + refrigerator(); + } else { + set_current_state(TASK_INTERRUPTIBLE); + spin_unlock_irq(&worker->lock); + if (!kthread_should_stop()) + schedule(); + __set_current_state(TASK_RUNNING); + } + } while (!kthread_should_stop()); + return 0; +} + +/* + * this will wait for all the worker threads to shutdown + */ +int btrfs_stop_workers(struct btrfs_workers *workers) +{ + struct list_head *cur; + struct btrfs_worker_thread *worker; + + list_splice_init(&workers->idle_list, &workers->worker_list); + while (!list_empty(&workers->worker_list)) { + cur = workers->worker_list.next; + worker = list_entry(cur, struct btrfs_worker_thread, + worker_list); + kthread_stop(worker->task); + list_del(&worker->worker_list); + kfree(worker); + } + return 0; +} + +/* + * simple init on struct btrfs_workers + */ +void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max) +{ + workers->num_workers = 0; + INIT_LIST_HEAD(&workers->worker_list); + INIT_LIST_HEAD(&workers->idle_list); + INIT_LIST_HEAD(&workers->order_list); + spin_lock_init(&workers->lock); + workers->max_workers = max; + workers->idle_thresh = 32; + workers->name = name; + workers->ordered = 0; +} + +/* + * starts new worker threads. This does not enforce the max worker + * count in case you need to temporarily go past it. + */ +int btrfs_start_workers(struct btrfs_workers *workers, int num_workers) +{ + struct btrfs_worker_thread *worker; + int ret = 0; + int i; + + for (i = 0; i < num_workers; i++) { + worker = kzalloc(sizeof(*worker), GFP_NOFS); + if (!worker) { + ret = -ENOMEM; + goto fail; + } + + INIT_LIST_HEAD(&worker->pending); + INIT_LIST_HEAD(&worker->worker_list); + spin_lock_init(&worker->lock); + atomic_set(&worker->num_pending, 0); + worker->task = kthread_run(worker_loop, worker, + "btrfs-%s-%d", workers->name, + workers->num_workers + i); + worker->workers = workers; + if (IS_ERR(worker->task)) { + kfree(worker); + ret = PTR_ERR(worker->task); + goto fail; + } + + spin_lock_irq(&workers->lock); + list_add_tail(&worker->worker_list, &workers->idle_list); + worker->idle = 1; + workers->num_workers++; + spin_unlock_irq(&workers->lock); + } + return 0; +fail: + btrfs_stop_workers(workers); + return ret; +} + +/* + * run through the list and find a worker thread that doesn't have a lot + * to do right now. This can return null if we aren't yet at the thread + * count limit and all of the threads are busy. + */ +static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers) +{ + struct btrfs_worker_thread *worker; + struct list_head *next; + int enforce_min = workers->num_workers < workers->max_workers; + + /* + * if we find an idle thread, don't move it to the end of the + * idle list. This improves the chance that the next submission + * will reuse the same thread, and maybe catch it while it is still + * working + */ + if (!list_empty(&workers->idle_list)) { + next = workers->idle_list.next; + worker = list_entry(next, struct btrfs_worker_thread, + worker_list); + return worker; + } + if (enforce_min || list_empty(&workers->worker_list)) + return NULL; + + /* + * if we pick a busy task, move the task to the end of the list. + * hopefully this will keep things somewhat evenly balanced. + * Do the move in batches based on the sequence number. This groups + * requests submitted at roughly the same time onto the same worker. + */ + next = workers->worker_list.next; + worker = list_entry(next, struct btrfs_worker_thread, worker_list); + atomic_inc(&worker->num_pending); + worker->sequence++; + + if (worker->sequence % workers->idle_thresh == 0) + list_move_tail(next, &workers->worker_list); + return worker; +} + +/* + * selects a worker thread to take the next job. This will either find + * an idle worker, start a new worker up to the max count, or just return + * one of the existing busy workers. + */ +static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers) +{ + struct btrfs_worker_thread *worker; + unsigned long flags; + +again: + spin_lock_irqsave(&workers->lock, flags); + worker = next_worker(workers); + spin_unlock_irqrestore(&workers->lock, flags); + + if (!worker) { + spin_lock_irqsave(&workers->lock, flags); + if (workers->num_workers >= workers->max_workers) { + struct list_head *fallback = NULL; + /* + * we have failed to find any workers, just + * return the force one + */ + if (!list_empty(&workers->worker_list)) + fallback = workers->worker_list.next; + if (!list_empty(&workers->idle_list)) + fallback = workers->idle_list.next; + BUG_ON(!fallback); + worker = list_entry(fallback, + struct btrfs_worker_thread, worker_list); + spin_unlock_irqrestore(&workers->lock, flags); + } else { + spin_unlock_irqrestore(&workers->lock, flags); + /* we're below the limit, start another worker */ + btrfs_start_workers(workers, 1); + goto again; + } + } + return worker; +} + +/* + * btrfs_requeue_work just puts the work item back on the tail of the list + * it was taken from. It is intended for use with long running work functions + * that make some progress and want to give the cpu up for others. + */ +int btrfs_requeue_work(struct btrfs_work *work) +{ + struct btrfs_worker_thread *worker = work->worker; + unsigned long flags; + + if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags)) + goto out; + + spin_lock_irqsave(&worker->lock, flags); + atomic_inc(&worker->num_pending); + list_add_tail(&work->list, &worker->pending); + + /* by definition we're busy, take ourselves off the idle + * list + */ + if (worker->idle) { + spin_lock_irqsave(&worker->workers->lock, flags); + worker->idle = 0; + list_move_tail(&worker->worker_list, + &worker->workers->worker_list); + spin_unlock_irqrestore(&worker->workers->lock, flags); + } + + spin_unlock_irqrestore(&worker->lock, flags); + +out: + return 0; +} + +/* + * places a struct btrfs_work into the pending queue of one of the kthreads + */ +int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work) +{ + struct btrfs_worker_thread *worker; + unsigned long flags; + int wake = 0; + + /* don't requeue something already on a list */ + if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags)) + goto out; + + worker = find_worker(workers); + if (workers->ordered) { + spin_lock_irqsave(&workers->lock, flags); + list_add_tail(&work->order_list, &workers->order_list); + spin_unlock_irqrestore(&workers->lock, flags); + } else { + INIT_LIST_HEAD(&work->order_list); + } + + spin_lock_irqsave(&worker->lock, flags); + atomic_inc(&worker->num_pending); + check_busy_worker(worker); + list_add_tail(&work->list, &worker->pending); + + /* + * avoid calling into wake_up_process if this thread has already + * been kicked + */ + if (!worker->working) + wake = 1; + worker->working = 1; + + spin_unlock_irqrestore(&worker->lock, flags); + + if (wake) + wake_up_process(worker->task); +out: + return 0; +} |