diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b9a5364..98ff4fb 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -31,6 +31,7 @@
 #include "btrfs_inode.h"
 #include "volumes.h"
 #include "print-tree.h"
+#include "async-thread.h"
 
 #if 0
 static int check_tree_block(struct btrfs_root *root, struct extent_buffer *buf)
@@ -46,8 +47,7 @@
 #endif
 
 static struct extent_io_ops btree_extent_io_ops;
-static struct workqueue_struct *end_io_workqueue;
-static struct workqueue_struct *async_submit_workqueue;
+static void end_workqueue_fn(struct btrfs_work *work);
 
 struct end_io_wq {
 	struct bio *bio;
@@ -57,6 +57,7 @@
 	int error;
 	int metadata;
 	struct list_head list;
+	struct btrfs_work work;
 };
 
 struct async_submit_bio {
@@ -66,6 +67,7 @@
 	extent_submit_bio_hook_t *submit_bio_hook;
 	int rw;
 	int mirror_num;
+	struct btrfs_work work;
 };
 
 struct extent_map *btree_get_extent(struct inode *inode, struct page *page,
@@ -389,7 +391,6 @@
 {
 	struct end_io_wq *end_io_wq = bio->bi_private;
 	struct btrfs_fs_info *fs_info;
-	unsigned long flags;
 
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
 	if (bio->bi_size)
@@ -397,11 +398,10 @@
 #endif
 
 	fs_info = end_io_wq->info;
-	spin_lock_irqsave(&fs_info->end_io_work_lock, flags);
 	end_io_wq->error = err;
-	list_add_tail(&end_io_wq->list, &fs_info->end_io_work_list);
-	spin_unlock_irqrestore(&fs_info->end_io_work_lock, flags);
-	queue_work(end_io_workqueue, &fs_info->end_io_work);
+	end_io_wq->work.func = end_workqueue_fn;
+	end_io_wq->work.flags = 0;
+	btrfs_queue_worker(&fs_info->endio_workers, &end_io_wq->work);
 
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
 	return 0;
@@ -428,6 +428,19 @@
 	return 0;
 }
 
+static void run_one_async_submit(struct btrfs_work *work)
+{
+	struct btrfs_fs_info *fs_info;
+	struct async_submit_bio *async;
+
+	async = container_of(work, struct  async_submit_bio, work);
+	fs_info = BTRFS_I(async->inode)->root->fs_info;
+	atomic_dec(&fs_info->nr_async_submits);
+	async->submit_bio_hook(async->inode, async->rw, async->bio,
+			       async->mirror_num);
+	kfree(async);
+}
+
 int btrfs_wq_submit_bio(struct btrfs_fs_info *fs_info, struct inode *inode,
 			int rw, struct bio *bio, int mirror_num,
 			extent_submit_bio_hook_t *submit_bio_hook)
@@ -443,13 +456,10 @@
 	async->bio = bio;
 	async->mirror_num = mirror_num;
 	async->submit_bio_hook = submit_bio_hook;
-
-	spin_lock(&fs_info->async_submit_work_lock);
-	list_add_tail(&async->list, &fs_info->async_submit_work_list);
+	async->work.func = run_one_async_submit;
+	async->work.flags = 0;
 	atomic_inc(&fs_info->nr_async_submits);
-	spin_unlock(&fs_info->async_submit_work_lock);
-
-	queue_work(async_submit_workqueue, &fs_info->async_submit_work);
+	btrfs_queue_worker(&fs_info->workers, &async->work);
 	return 0;
 }
 
@@ -462,19 +472,32 @@
 
 	offset = bio->bi_sector << 9;
 
+	/*
+	 * when we're called for a write, we're already in the async
+	 * submission context.  Just jump ingo btrfs_map_bio
+	 */
 	if (rw & (1 << BIO_RW)) {
-		return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio, mirror_num);
+		return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio,
+				     mirror_num, 0);
 	}
 
+	/*
+	 * called for a read, do the setup so that checksum validation
+	 * can happen in the async kernel threads
+	 */
 	ret = btrfs_bio_wq_end_io(root->fs_info, bio, 1);
 	BUG_ON(ret);
 
-	return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio, mirror_num);
+	return btrfs_map_bio(BTRFS_I(inode)->root, rw, bio, mirror_num, 1);
 }
 
 static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
 				 int mirror_num)
 {
+	/*
+	 * kthread helpers are used to submit writes so that checksumming
+	 * can happen in parallel across all CPUs
+	 */
 	if (!(rw & (1 << BIO_RW))) {
 		return __btree_submit_bio_hook(inode, rw, bio, mirror_num);
 	}
@@ -1036,95 +1059,40 @@
 	return ret;
 }
 
-#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
-static void btrfs_end_io_csum(void *p)
-#else
-static void btrfs_end_io_csum(struct work_struct *work)
-#endif
+/*
+ * called by the kthread helper functions to finally call the bio end_io
+ * functions.  This is where read checksum verification actually happens
+ */
+static void end_workqueue_fn(struct btrfs_work *work)
 {
-#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
-	struct btrfs_fs_info *fs_info = p;
-#else
-	struct btrfs_fs_info *fs_info = container_of(work,
-						     struct btrfs_fs_info,
-						     end_io_work);
-#endif
-	unsigned long flags;
-	struct end_io_wq *end_io_wq;
 	struct bio *bio;
-	struct list_head *next;
+	struct end_io_wq *end_io_wq;
+	struct btrfs_fs_info *fs_info;
 	int error;
-	int was_empty;
 
-	while(1) {
-		spin_lock_irqsave(&fs_info->end_io_work_lock, flags);
-		if (list_empty(&fs_info->end_io_work_list)) {
-			spin_unlock_irqrestore(&fs_info->end_io_work_lock,
-					       flags);
-			return;
-		}
-		next = fs_info->end_io_work_list.next;
-		list_del(next);
-		spin_unlock_irqrestore(&fs_info->end_io_work_lock, flags);
+	end_io_wq = container_of(work, struct end_io_wq, work);
+	bio = end_io_wq->bio;
+	fs_info = end_io_wq->info;
 
-		end_io_wq = list_entry(next, struct end_io_wq, list);
-
-		bio = end_io_wq->bio;
-		if (end_io_wq->metadata && !bio_ready_for_csum(bio)) {
-			spin_lock_irqsave(&fs_info->end_io_work_lock, flags);
-			was_empty = list_empty(&fs_info->end_io_work_list);
-			list_add_tail(&end_io_wq->list,
-				      &fs_info->end_io_work_list);
-			spin_unlock_irqrestore(&fs_info->end_io_work_lock,
-					       flags);
-			if (was_empty)
-				return;
-			continue;
-		}
-		error = end_io_wq->error;
-		bio->bi_private = end_io_wq->private;
-		bio->bi_end_io = end_io_wq->end_io;
-		kfree(end_io_wq);
+	/* metadata bios are special because the whole tree block must
+	 * be checksummed at once.  This makes sure the entire block is in
+	 * ram and up to date before trying to verify things.  For
+	 * blocksize <= pagesize, it is basically a noop
+	 */
+	if (end_io_wq->metadata && !bio_ready_for_csum(bio)) {
+		btrfs_queue_worker(&fs_info->endio_workers,
+				   &end_io_wq->work);
+		return;
+	}
+	error = end_io_wq->error;
+	bio->bi_private = end_io_wq->private;
+	bio->bi_end_io = end_io_wq->end_io;
+	kfree(end_io_wq);
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,23)
-		bio_endio(bio, bio->bi_size, error);
+	bio_endio(bio, bio->bi_size, error);
 #else
-		bio_endio(bio, error);
+	bio_endio(bio, error);
 #endif
-	}
-}
-
-#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
-static void btrfs_async_submit_work(void *p)
-#else
-static void btrfs_async_submit_work(struct work_struct *work)
-#endif
-{
-#if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
-	struct btrfs_fs_info *fs_info = p;
-#else
-	struct btrfs_fs_info *fs_info = container_of(work,
-						     struct btrfs_fs_info,
-						     async_submit_work);
-#endif
-	struct async_submit_bio *async;
-	struct list_head *next;
-
-	while(1) {
-		spin_lock(&fs_info->async_submit_work_lock);
-		if (list_empty(&fs_info->async_submit_work_list)) {
-			spin_unlock(&fs_info->async_submit_work_lock);
-			return;
-		}
-		next = fs_info->async_submit_work_list.next;
-		list_del(next);
-		atomic_dec(&fs_info->nr_async_submits);
-		spin_unlock(&fs_info->async_submit_work_lock);
-
-		async = list_entry(next, struct async_submit_bio, list);
-		async->submit_bio_hook(async->inode, async->rw, async->bio,
-				       async->mirror_num);
-		kfree(async);
-	}
 }
 
 struct btrfs_root *open_ctree(struct super_block *sb,
@@ -1155,19 +1123,11 @@
 		err = -ENOMEM;
 		goto fail;
 	}
-	end_io_workqueue = create_workqueue("btrfs-end-io");
-	BUG_ON(!end_io_workqueue);
-	async_submit_workqueue = create_workqueue("btrfs-async-submit");
-
 	INIT_RADIX_TREE(&fs_info->fs_roots_radix, GFP_NOFS);
 	INIT_LIST_HEAD(&fs_info->trans_list);
 	INIT_LIST_HEAD(&fs_info->dead_roots);
 	INIT_LIST_HEAD(&fs_info->hashers);
-	INIT_LIST_HEAD(&fs_info->end_io_work_list);
-	INIT_LIST_HEAD(&fs_info->async_submit_work_list);
 	spin_lock_init(&fs_info->hash_lock);
-	spin_lock_init(&fs_info->end_io_work_lock);
-	spin_lock_init(&fs_info->async_submit_work_lock);
 	spin_lock_init(&fs_info->delalloc_lock);
 	spin_lock_init(&fs_info->new_trans_lock);
 
@@ -1222,13 +1182,8 @@
 	fs_info->do_barriers = 1;
 
 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
-	INIT_WORK(&fs_info->end_io_work, btrfs_end_io_csum, fs_info);
-	INIT_WORK(&fs_info->async_submit_work, btrfs_async_submit_work,
-		  fs_info);
 	INIT_WORK(&fs_info->trans_work, btrfs_transaction_cleaner, fs_info);
 #else
-	INIT_WORK(&fs_info->end_io_work, btrfs_end_io_csum);
-	INIT_WORK(&fs_info->async_submit_work, btrfs_async_submit_work);
 	INIT_DELAYED_WORK(&fs_info->trans_work, btrfs_transaction_cleaner);
 #endif
 	BTRFS_I(fs_info->btree_inode)->root = tree_root;
@@ -1240,6 +1195,19 @@
 	mutex_init(&fs_info->trans_mutex);
 	mutex_init(&fs_info->fs_mutex);
 
+	/* we need to start all the end_io workers up front because the
+	 * queue work function gets called at interrupt time.  The endio
+	 * workers don't normally start IO, so some number of them <= the
+	 * number of cpus is fine.  They handle checksumming after a read.
+	 *
+	 * The other worker threads do start IO, so the max is larger than
+	 * the number of CPUs.  FIXME, tune this for huge machines
+	 */
+	btrfs_init_workers(&fs_info->workers, num_online_cpus() * 2);
+	btrfs_init_workers(&fs_info->endio_workers, num_online_cpus());
+	btrfs_start_workers(&fs_info->workers, 1);
+	btrfs_start_workers(&fs_info->endio_workers, num_online_cpus());
+
 #if 0
 	ret = add_hasher(fs_info, "crc32c");
 	if (ret) {
@@ -1375,6 +1343,8 @@
 	extent_io_tree_empty_lru(&BTRFS_I(fs_info->btree_inode)->io_tree);
 fail_iput:
 	iput(fs_info->btree_inode);
+	btrfs_stop_workers(&fs_info->workers);
+	btrfs_stop_workers(&fs_info->endio_workers);
 fail:
 	btrfs_close_devices(fs_info->fs_devices);
 	btrfs_mapping_tree_free(&fs_info->mapping_tree);
@@ -1623,16 +1593,10 @@
 	extent_io_tree_empty_lru(&fs_info->extent_ins);
 	extent_io_tree_empty_lru(&BTRFS_I(fs_info->btree_inode)->io_tree);
 
-	flush_workqueue(async_submit_workqueue);
-	flush_workqueue(end_io_workqueue);
-
 	truncate_inode_pages(fs_info->btree_inode->i_mapping, 0);
 
-	flush_workqueue(async_submit_workqueue);
-	destroy_workqueue(async_submit_workqueue);
-
-	flush_workqueue(end_io_workqueue);
-	destroy_workqueue(end_io_workqueue);
+	btrfs_stop_workers(&fs_info->workers);
+	btrfs_stop_workers(&fs_info->endio_workers);
 
 	iput(fs_info->btree_inode);
 #if 0