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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 2008-06-11 20:21:24 -04:00
parent d05e5a4dad
commit 35d8ba6629
2 changed files with 73 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

100
fs/btrfs/async-thread.c
View File

@ -34,6 +34,9 @@
* 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;
@ -51,8 +54,44 @@ struct btrfs_worker_thread {
/* 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);
}
}
/*
* main loop for servicing work items
*/
@ -76,6 +115,7 @@ static int worker_loop(void *arg)
atomic_dec(&worker->num_pending);
spin_lock_irq(&worker->lock);
check_idle_worker(worker);
}
worker->working = 0;
if (freezing(current)) {
@ -98,6 +138,7 @@ 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,
@ -116,9 +157,10 @@ void btrfs_init_workers(struct btrfs_workers *workers, int max)
{
workers->num_workers = 0;
INIT_LIST_HEAD(&workers->worker_list);
workers->last = NULL;
INIT_LIST_HEAD(&workers->idle_list);
spin_lock_init(&workers->lock);
workers->max_workers = max;
workers->idle_thresh = 64;
}
/*
@ -143,14 +185,14 @@ int btrfs_start_workers(struct btrfs_workers *workers, int num_workers)
spin_lock_init(&worker->lock);
atomic_set(&worker->num_pending, 0);
worker->task = kthread_run(worker_loop, worker, "btrfs");
worker->workers = workers;
if (IS_ERR(worker->task)) {
ret = PTR_ERR(worker->task);
goto fail;
}
spin_lock_irq(&workers->lock);
list_add_tail(&worker->worker_list, &workers->worker_list);
workers->last = worker;
list_add_tail(&worker->worker_list, &workers->idle_list);
workers->num_workers++;
spin_unlock_irq(&workers->lock);
}
@ -169,42 +211,30 @@ static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
{
struct btrfs_worker_thread *worker;
struct list_head *next;
struct list_head *start;
int enforce_min = workers->num_workers < workers->max_workers;
/* start with the last thread if it isn't busy */
worker = workers->last;
if (atomic_read(&worker->num_pending) < 64)
goto done;
next = worker->worker_list.next;
start = &worker->worker_list;
/*
* check all the workers for someone that is bored. FIXME, do
* something smart here
* 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
*/
while(next != start) {
if (next == &workers->worker_list) {
next = workers->worker_list.next;
continue;
}
if (!list_empty(&workers->idle_list)) {
next = workers->idle_list.next;
worker = list_entry(next, struct btrfs_worker_thread,
worker_list);
if (atomic_read(&worker->num_pending) < 64 || !enforce_min)
goto done;
next = next->next;
return worker;
}
if (enforce_min || list_empty(&workers->worker_list))
return NULL;
/*
* nobody was bored, if we're already at the max thread count,
* use the last thread
* if we pick a busy task, move the task to the end of the list.
* hopefully this will keep things somewhat evenly balanced
*/
if (!enforce_min || atomic_read(&workers->last->num_pending) < 64) {
return workers->last;
}
return NULL;
done:
workers->last = worker;
next = workers->worker_list.next;
worker = list_entry(next, struct btrfs_worker_thread, worker_list);
list_move_tail(next, &workers->worker_list);
return worker;
}
@ -221,11 +251,17 @@ again:
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
*/
worker = list_entry(workers->worker_list.next,
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 {
@ -254,6 +290,7 @@ int btrfs_requeue_work(struct btrfs_work *work)
spin_lock_irqsave(&worker->lock, flags);
atomic_inc(&worker->num_pending);
list_add_tail(&work->list, &worker->pending);
check_busy_worker(worker);
spin_unlock_irqrestore(&worker->lock, flags);
out:
return 0;
@ -276,6 +313,7 @@ int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
spin_lock_irqsave(&worker->lock, flags);
atomic_inc(&worker->num_pending);
check_busy_worker(worker);
list_add_tail(&work->list, &worker->pending);
/*

7
fs/btrfs/async-thread.h
View File

@ -60,11 +60,12 @@ struct btrfs_workers {
/* 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;
/* list with all the work threads */
struct list_head worker_list;
/* the last worker thread to have something queued */
struct btrfs_worker_thread *last;
struct list_head idle_list;
/* lock for finding the next worker thread to queue on */
spinlock_t lock;