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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>
104 lines
3.3 KiB
C
104 lines
3.3 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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#ifndef __BTRFS_ASYNC_THREAD_
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#define __BTRFS_ASYNC_THREAD_
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struct btrfs_worker_thread;
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/*
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* This is similar to a workqueue, but it is meant to spread the operations
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* across all available cpus instead of just the CPU that was used to
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* queue the work. There is also some batching introduced to try and
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* cut down on context switches.
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*
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* By default threads are added on demand up to 2 * the number of cpus.
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* Changing struct btrfs_workers->max_workers is one way to prevent
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* demand creation of kthreads.
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*
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* the basic model of these worker threads is to embed a btrfs_work
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* structure in your own data struct, and use container_of in a
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* work function to get back to your data struct.
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*/
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struct btrfs_work {
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/*
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* func should be set to the function you want called
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* your work struct is passed as the only arg
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*
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* ordered_func must be set for work sent to an ordered work queue,
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* and it is called to complete a given work item in the same
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* order they were sent to the queue.
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*/
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void (*func)(struct btrfs_work *work);
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void (*ordered_func)(struct btrfs_work *work);
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void (*ordered_free)(struct btrfs_work *work);
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/*
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* flags should be set to zero. It is used to make sure the
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* struct is only inserted once into the list.
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*/
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unsigned long flags;
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/* don't touch these */
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struct btrfs_worker_thread *worker;
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struct list_head list;
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struct list_head order_list;
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};
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struct btrfs_workers {
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/* current number of running workers */
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int num_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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/* force completions in the order they were queued */
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int ordered;
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/* list with all the work threads. The workers on the idle thread
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* may be actively servicing jobs, but they haven't yet hit the
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* idle thresh limit above.
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*/
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struct list_head worker_list;
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struct list_head idle_list;
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/*
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* when operating in ordered mode, this maintains the list
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* of work items waiting for completion
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*/
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struct list_head order_list;
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struct list_head prio_order_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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/* extra name for this worker, used for current->name */
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char *name;
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};
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int btrfs_queue_worker(struct btrfs_workers *workers, struct btrfs_work *work);
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int btrfs_start_workers(struct btrfs_workers *workers, int num_workers);
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int btrfs_stop_workers(struct btrfs_workers *workers);
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void btrfs_init_workers(struct btrfs_workers *workers, char *name, int max);
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int btrfs_requeue_work(struct btrfs_work *work);
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void btrfs_set_work_high_prio(struct btrfs_work *work);
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#endif
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