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d313d7a31a
Btrfs is using WRITE_SYNC_PLUG to send down synchronous IOs with a higher priority. But, the checksumming helper threads prevent it from being fully effective. There are two problems. First, a big queue of pending checksumming will delay the synchronous IO behind other lower priority writes. Second, the checksumming uses an ordered async work queue. The ordering makes sure that IOs are sent to the block layer in the same order they are sent to the checksumming threads. Usually this gives us less seeky IO. But, when we start mixing IO priorities, the lower priority IO can delay the higher priority IO. This patch solves both problems by adding a high priority list to the async helper threads, and a new btrfs_set_work_high_prio(), which is used to make put a new async work item onto the higher priority list. The ordering is still done on high priority IO, but all of the high priority bios are ordered separately from the low priority bios. This ordering is purely an IO optimization, it is not involved in data or metadata integrity. Signed-off-by: Chris Mason <chris.mason@oracle.com>
502 lines
13 KiB
C
502 lines
13 KiB
C
/*
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* Copyright (C) 2007 Oracle. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License v2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 021110-1307, USA.
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*/
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#include <linux/kthread.h>
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#include <linux/list.h>
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#include <linux/spinlock.h>
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#include <linux/freezer.h>
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#include "async-thread.h"
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#define WORK_QUEUED_BIT 0
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#define WORK_DONE_BIT 1
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#define WORK_ORDER_DONE_BIT 2
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#define WORK_HIGH_PRIO_BIT 3
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/*
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* container for the kthread task pointer and the list of pending work
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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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struct list_head prio_pending;
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/* list of worker threads from struct btrfs_workers */
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struct list_head worker_list;
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/* kthread */
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struct task_struct *task;
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/* number of things on the pending list */
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atomic_t num_pending;
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unsigned long sequence;
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/* protects the pending list. */
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spinlock_t lock;
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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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static noinline int run_ordered_completions(struct btrfs_workers *workers,
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struct btrfs_work *work)
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{
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unsigned long flags;
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if (!workers->ordered)
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return 0;
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set_bit(WORK_DONE_BIT, &work->flags);
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spin_lock_irqsave(&workers->lock, flags);
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while (1) {
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if (!list_empty(&workers->prio_order_list)) {
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work = list_entry(workers->prio_order_list.next,
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struct btrfs_work, order_list);
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} else if (!list_empty(&workers->order_list)) {
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work = list_entry(workers->order_list.next,
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struct btrfs_work, order_list);
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} else {
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break;
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}
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if (!test_bit(WORK_DONE_BIT, &work->flags))
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break;
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/* we are going to call the ordered done function, but
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* we leave the work item on the list as a barrier so
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* that later work items that are done don't have their
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* functions called before this one returns
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*/
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if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
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break;
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spin_unlock_irqrestore(&workers->lock, flags);
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work->ordered_func(work);
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/* now take the lock again and call the freeing code */
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spin_lock_irqsave(&workers->lock, flags);
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list_del(&work->order_list);
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work->ordered_free(work);
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}
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spin_unlock_irqrestore(&workers->lock, flags);
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return 0;
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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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static int worker_loop(void *arg)
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{
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struct btrfs_worker_thread *worker = arg;
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struct list_head *cur;
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struct btrfs_work *work;
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do {
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spin_lock_irq(&worker->lock);
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again_locked:
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while (1) {
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if (!list_empty(&worker->prio_pending))
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cur = worker->prio_pending.next;
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else if (!list_empty(&worker->pending))
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cur = worker->pending.next;
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else
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break;
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work = list_entry(cur, struct btrfs_work, list);
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list_del(&work->list);
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clear_bit(WORK_QUEUED_BIT, &work->flags);
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work->worker = worker;
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spin_unlock_irq(&worker->lock);
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work->func(work);
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atomic_dec(&worker->num_pending);
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/*
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* unless this is an ordered work queue,
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* 'work' was probably freed by func above.
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*/
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run_ordered_completions(worker->workers, work);
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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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if (freezing(current)) {
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worker->working = 0;
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spin_unlock_irq(&worker->lock);
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refrigerator();
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} else {
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spin_unlock_irq(&worker->lock);
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if (!kthread_should_stop()) {
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cpu_relax();
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/*
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* we've dropped the lock, did someone else
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* jump_in?
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*/
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smp_mb();
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if (!list_empty(&worker->pending) ||
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!list_empty(&worker->prio_pending))
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continue;
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/*
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* this short schedule allows more work to
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* come in without the queue functions
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* needing to go through wake_up_process()
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*
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* worker->working is still 1, so nobody
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* is going to try and wake us up
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*/
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schedule_timeout(1);
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smp_mb();
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if (!list_empty(&worker->pending) ||
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!list_empty(&worker->prio_pending))
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continue;
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if (kthread_should_stop())
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break;
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/* still no more work?, sleep for real */
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spin_lock_irq(&worker->lock);
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set_current_state(TASK_INTERRUPTIBLE);
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if (!list_empty(&worker->pending) ||
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!list_empty(&worker->prio_pending))
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goto again_locked;
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/*
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* this makes sure we get a wakeup when someone
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* adds something new to the queue
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*/
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worker->working = 0;
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spin_unlock_irq(&worker->lock);
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if (!kthread_should_stop())
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schedule();
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}
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__set_current_state(TASK_RUNNING);
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}
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} while (!kthread_should_stop());
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return 0;
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}
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/*
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* this will wait for all the worker threads to shutdown
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*/
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int btrfs_stop_workers(struct btrfs_workers *workers)
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{
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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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worker_list);
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kthread_stop(worker->task);
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list_del(&worker->worker_list);
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kfree(worker);
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}
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return 0;
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}
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/*
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* simple init on struct btrfs_workers
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*/
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void btrfs_init_workers(struct btrfs_workers *workers, char *name, 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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INIT_LIST_HEAD(&workers->idle_list);
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INIT_LIST_HEAD(&workers->order_list);
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INIT_LIST_HEAD(&workers->prio_order_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 = 32;
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workers->name = name;
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workers->ordered = 0;
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}
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/*
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* starts new worker threads. This does not enforce the max worker
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* count in case you need to temporarily go past it.
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*/
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int btrfs_start_workers(struct btrfs_workers *workers, int num_workers)
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{
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struct btrfs_worker_thread *worker;
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int ret = 0;
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int i;
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for (i = 0; i < num_workers; i++) {
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worker = kzalloc(sizeof(*worker), GFP_NOFS);
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if (!worker) {
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ret = -ENOMEM;
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goto fail;
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}
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INIT_LIST_HEAD(&worker->pending);
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INIT_LIST_HEAD(&worker->prio_pending);
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INIT_LIST_HEAD(&worker->worker_list);
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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,
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"btrfs-%s-%d", workers->name,
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workers->num_workers + i);
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worker->workers = workers;
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if (IS_ERR(worker->task)) {
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kfree(worker);
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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->idle_list);
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worker->idle = 1;
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workers->num_workers++;
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spin_unlock_irq(&workers->lock);
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}
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return 0;
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fail:
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btrfs_stop_workers(workers);
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return ret;
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}
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/*
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* run through the list and find a worker thread that doesn't have a lot
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* to do right now. This can return null if we aren't yet at the thread
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* count limit and all of the threads are busy.
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*/
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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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int enforce_min = workers->num_workers < workers->max_workers;
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/*
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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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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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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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* 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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* Do the move in batches based on the sequence number. This groups
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* requests submitted at roughly the same time onto the same worker.
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*/
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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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atomic_inc(&worker->num_pending);
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worker->sequence++;
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if (worker->sequence % workers->idle_thresh == 0)
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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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/*
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* selects a worker thread to take the next job. This will either find
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* an idle worker, start a new worker up to the max count, or just return
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* one of the existing busy workers.
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*/
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static struct btrfs_worker_thread *find_worker(struct btrfs_workers *workers)
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{
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struct btrfs_worker_thread *worker;
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unsigned long flags;
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again:
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spin_lock_irqsave(&workers->lock, flags);
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worker = next_worker(workers);
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spin_unlock_irqrestore(&workers->lock, flags);
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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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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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spin_unlock_irqrestore(&workers->lock, flags);
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/* we're below the limit, start another worker */
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btrfs_start_workers(workers, 1);
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goto again;
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}
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}
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return worker;
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}
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/*
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* btrfs_requeue_work just puts the work item back on the tail of the list
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* it was taken from. It is intended for use with long running work functions
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* that make some progress and want to give the cpu up for others.
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*/
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int btrfs_requeue_work(struct btrfs_work *work)
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{
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struct btrfs_worker_thread *worker = work->worker;
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unsigned long flags;
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int wake = 0;
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if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
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goto out;
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spin_lock_irqsave(&worker->lock, flags);
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if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
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list_add_tail(&work->list, &worker->prio_pending);
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else
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list_add_tail(&work->list, &worker->pending);
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atomic_inc(&worker->num_pending);
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/* by definition we're busy, take ourselves off the idle
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* list
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*/
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if (worker->idle) {
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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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if (!worker->working) {
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wake = 1;
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worker->working = 1;
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}
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spin_unlock_irqrestore(&worker->lock, flags);
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if (wake)
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wake_up_process(worker->task);
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out:
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return 0;
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}
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void btrfs_set_work_high_prio(struct btrfs_work *work)
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{
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set_bit(WORK_HIGH_PRIO_BIT, &work->flags);
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}
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/*
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* places a struct btrfs_work into the pending queue of one of the kthreads
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*/
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int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work)
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{
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struct btrfs_worker_thread *worker;
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unsigned long flags;
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int wake = 0;
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/* don't requeue something already on a list */
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if (test_and_set_bit(WORK_QUEUED_BIT, &work->flags))
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goto out;
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worker = find_worker(workers);
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if (workers->ordered) {
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spin_lock_irqsave(&workers->lock, flags);
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if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags)) {
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list_add_tail(&work->order_list,
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&workers->prio_order_list);
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} else {
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list_add_tail(&work->order_list, &workers->order_list);
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}
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spin_unlock_irqrestore(&workers->lock, flags);
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} else {
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INIT_LIST_HEAD(&work->order_list);
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}
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spin_lock_irqsave(&worker->lock, flags);
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if (test_bit(WORK_HIGH_PRIO_BIT, &work->flags))
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list_add_tail(&work->list, &worker->prio_pending);
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else
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list_add_tail(&work->list, &worker->pending);
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atomic_inc(&worker->num_pending);
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check_busy_worker(worker);
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/*
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* avoid calling into wake_up_process if this thread has already
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* been kicked
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*/
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if (!worker->working)
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wake = 1;
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worker->working = 1;
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spin_unlock_irqrestore(&worker->lock, flags);
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if (wake)
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wake_up_process(worker->task);
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out:
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return 0;
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}
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