Btrfs: Worker thread optimizations
This changes the worker thread pool to maintain a list of idle threads, avoiding a complex search for a good thread to wake up. Threads have two states: idle - we try to reuse the last thread used in hopes of improving the batching ratios busy - each time a new work item is added to a busy task, the task is rotated to the end of the line. Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason
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d05e5a4dad
Коммит
35d8ba6629
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@ -34,6 +34,9 @@
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* One of these is allocated per thread.
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*/
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struct btrfs_worker_thread {
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/* pool we belong to */
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struct btrfs_workers *workers;
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/* list of struct btrfs_work that are waiting for service */
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struct list_head pending;
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@ -51,8 +54,44 @@ struct btrfs_worker_thread {
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/* set to non-zero when this thread is already awake and kicking */
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int working;
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/* are we currently idle */
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int idle;
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};
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/*
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* helper function to move a thread onto the idle list after it
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* has finished some requests.
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*/
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static void check_idle_worker(struct btrfs_worker_thread *worker)
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{
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if (!worker->idle && atomic_read(&worker->num_pending) <
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worker->workers->idle_thresh / 2) {
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unsigned long flags;
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spin_lock_irqsave(&worker->workers->lock, flags);
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worker->idle = 1;
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list_move(&worker->worker_list, &worker->workers->idle_list);
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spin_unlock_irqrestore(&worker->workers->lock, flags);
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}
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}
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/*
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* helper function to move a thread off the idle list after new
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* pending work is added.
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*/
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static void check_busy_worker(struct btrfs_worker_thread *worker)
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{
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if (worker->idle && atomic_read(&worker->num_pending) >=
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worker->workers->idle_thresh) {
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unsigned long flags;
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spin_lock_irqsave(&worker->workers->lock, flags);
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worker->idle = 0;
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list_move_tail(&worker->worker_list,
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&worker->workers->worker_list);
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spin_unlock_irqrestore(&worker->workers->lock, flags);
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}
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}
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/*
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* main loop for servicing work items
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*/
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@ -76,6 +115,7 @@ static int worker_loop(void *arg)
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atomic_dec(&worker->num_pending);
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spin_lock_irq(&worker->lock);
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check_idle_worker(worker);
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}
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worker->working = 0;
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if (freezing(current)) {
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@ -98,6 +138,7 @@ int btrfs_stop_workers(struct btrfs_workers *workers)
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struct list_head *cur;
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struct btrfs_worker_thread *worker;
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list_splice_init(&workers->idle_list, &workers->worker_list);
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while(!list_empty(&workers->worker_list)) {
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cur = workers->worker_list.next;
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worker = list_entry(cur, struct btrfs_worker_thread,
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@ -116,9 +157,10 @@ void btrfs_init_workers(struct btrfs_workers *workers, int max)
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{
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workers->num_workers = 0;
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INIT_LIST_HEAD(&workers->worker_list);
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workers->last = NULL;
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INIT_LIST_HEAD(&workers->idle_list);
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spin_lock_init(&workers->lock);
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workers->max_workers = max;
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workers->idle_thresh = 64;
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}
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/*
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@ -143,14 +185,14 @@ int btrfs_start_workers(struct btrfs_workers *workers, int num_workers)
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spin_lock_init(&worker->lock);
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atomic_set(&worker->num_pending, 0);
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worker->task = kthread_run(worker_loop, worker, "btrfs");
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worker->workers = workers;
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if (IS_ERR(worker->task)) {
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ret = PTR_ERR(worker->task);
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goto fail;
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}
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spin_lock_irq(&workers->lock);
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list_add_tail(&worker->worker_list, &workers->worker_list);
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workers->last = worker;
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list_add_tail(&worker->worker_list, &workers->idle_list);
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workers->num_workers++;
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spin_unlock_irq(&workers->lock);
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}
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@ -169,42 +211,30 @@ static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
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{
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struct btrfs_worker_thread *worker;
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struct list_head *next;
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struct list_head *start;
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int enforce_min = workers->num_workers < workers->max_workers;
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/* start with the last thread if it isn't busy */
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worker = workers->last;
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if (atomic_read(&worker->num_pending) < 64)
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goto done;
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next = worker->worker_list.next;
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start = &worker->worker_list;
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/*
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* check all the workers for someone that is bored. FIXME, do
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* something smart here
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* if we find an idle thread, don't move it to the end of the
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* idle list. This improves the chance that the next submission
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* will reuse the same thread, and maybe catch it while it is still
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* working
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*/
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while(next != start) {
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if (next == &workers->worker_list) {
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next = workers->worker_list.next;
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continue;
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}
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if (!list_empty(&workers->idle_list)) {
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next = workers->idle_list.next;
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worker = list_entry(next, struct btrfs_worker_thread,
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worker_list);
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if (atomic_read(&worker->num_pending) < 64 || !enforce_min)
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goto done;
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next = next->next;
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return worker;
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}
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if (enforce_min || list_empty(&workers->worker_list))
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return NULL;
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/*
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* nobody was bored, if we're already at the max thread count,
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* use the last thread
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* if we pick a busy task, move the task to the end of the list.
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* hopefully this will keep things somewhat evenly balanced
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*/
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if (!enforce_min || atomic_read(&workers->last->num_pending) < 64) {
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return workers->last;
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}
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return NULL;
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done:
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workers->last = worker;
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next = workers->worker_list.next;
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worker = list_entry(next, struct btrfs_worker_thread, worker_list);
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list_move_tail(next, &workers->worker_list);
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return worker;
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}
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@ -221,11 +251,17 @@ again:
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if (!worker) {
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spin_lock_irqsave(&workers->lock, flags);
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if (workers->num_workers >= workers->max_workers) {
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struct list_head *fallback = NULL;
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/*
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* we have failed to find any workers, just
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* return the force one
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*/
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worker = list_entry(workers->worker_list.next,
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if (!list_empty(&workers->worker_list))
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fallback = workers->worker_list.next;
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if (!list_empty(&workers->idle_list))
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fallback = workers->idle_list.next;
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BUG_ON(!fallback);
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worker = list_entry(fallback,
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struct btrfs_worker_thread, worker_list);
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spin_unlock_irqrestore(&workers->lock, flags);
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} else {
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@ -254,6 +290,7 @@ int btrfs_requeue_work(struct btrfs_work *work)
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spin_lock_irqsave(&worker->lock, flags);
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atomic_inc(&worker->num_pending);
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list_add_tail(&work->list, &worker->pending);
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check_busy_worker(worker);
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spin_unlock_irqrestore(&worker->lock, flags);
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out:
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return 0;
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@ -276,6 +313,7 @@ int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
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spin_lock_irqsave(&worker->lock, flags);
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atomic_inc(&worker->num_pending);
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check_busy_worker(worker);
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list_add_tail(&work->list, &worker->pending);
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/*
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@ -60,11 +60,12 @@ struct btrfs_workers {
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/* max number of workers allowed. changed by btrfs_start_workers */
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int max_workers;
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/* once a worker has this many requests or fewer, it is idle */
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int idle_thresh;
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/* list with all the work threads */
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struct list_head worker_list;
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/* the last worker thread to have something queued */
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struct btrfs_worker_thread *last;
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struct list_head idle_list;
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/* lock for finding the next worker thread to queue on */
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spinlock_t lock;
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