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Btrfs: add a plugging callback to raid56 writes 

Buffered writes and DIRECT_IO writes will often break up
big contiguous changes to the file into sub-stripe writes.

This adds a plugging callback to gather those smaller writes full stripe
writes.

Example on flash:

fio job to do 64K writes in batches of 3 (which makes a full stripe):

With plugging: 450MB/s
Without plugging: 220MB/s

Signed-off-by: Chris Mason <chris.mason@fusionio.com>
This commit is contained in:
Chris Mason 2013-01-31 14:42:28 -05:00
parent 4ae10b3a13
commit 6ac0f4884e
1 changed files with 124 additions and 4 deletions
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128
fs/btrfs/raid56.c
View File

@ -97,9 +97,10 @@ struct btrfs_raid_bio {
struct bio_list bio_list;
spinlock_t bio_list_lock;
/*
* also protected by the bio_list_lock, the
* stripe locking code uses plug_list to hand off
/* also protected by the bio_list_lock, the
* plug list is used by the plugging code
* to collect partial bios while plugged. The
* stripe locking code also uses it to hand off
* the stripe lock to the next pending IO
*/
struct list_head plug_list;
@ -1557,6 +1558,103 @@ static int __raid56_parity_write(struct btrfs_raid_bio *rbio)
return full_stripe_write(rbio);
}
/*
* We use plugging call backs to collect full stripes.
* Any time we get a partial stripe write while plugged
* we collect it into a list. When the unplug comes down,
* we sort the list by logical block number and merge
* everything we can into the same rbios
*/
struct btrfs_plug_cb {
struct blk_plug_cb cb;
struct btrfs_fs_info *info;
struct list_head rbio_list;
struct btrfs_work work;
};
/*
* rbios on the plug list are sorted for easier merging.
*/
static int plug_cmp(void *priv, struct list_head *a, struct list_head *b)
{
struct btrfs_raid_bio *ra = container_of(a, struct btrfs_raid_bio,
plug_list);
struct btrfs_raid_bio *rb = container_of(b, struct btrfs_raid_bio,
plug_list);
u64 a_sector = ra->bio_list.head->bi_sector;
u64 b_sector = rb->bio_list.head->bi_sector;
if (a_sector < b_sector)
return -1;
if (a_sector > b_sector)
return 1;
return 0;
}
static void run_plug(struct btrfs_plug_cb *plug)
{
struct btrfs_raid_bio *cur;
struct btrfs_raid_bio *last = NULL;
/*
* sort our plug list then try to merge
* everything we can in hopes of creating full
* stripes.
*/
list_sort(NULL, &plug->rbio_list, plug_cmp);
while (!list_empty(&plug->rbio_list)) {
cur = list_entry(plug->rbio_list.next,
struct btrfs_raid_bio, plug_list);
list_del_init(&cur->plug_list);
if (rbio_is_full(cur)) {
/* we have a full stripe, send it down */
full_stripe_write(cur);
continue;
}
if (last) {
if (rbio_can_merge(last, cur)) {
merge_rbio(last, cur);
__free_raid_bio(cur);
continue;
}
__raid56_parity_write(last);
}
last = cur;
}
if (last) {
__raid56_parity_write(last);
}
kfree(plug);
}
/*
* if the unplug comes from schedule, we have to push the
* work off to a helper thread
*/
static void unplug_work(struct btrfs_work *work)
{
struct btrfs_plug_cb *plug;
plug = container_of(work, struct btrfs_plug_cb, work);
run_plug(plug);
}
static void btrfs_raid_unplug(struct blk_plug_cb *cb, bool from_schedule)
{
struct btrfs_plug_cb *plug;
plug = container_of(cb, struct btrfs_plug_cb, cb);
if (from_schedule) {
plug->work.flags = 0;
plug->work.func = unplug_work;
btrfs_queue_worker(&plug->info->rmw_workers,
&plug->work);
return;
}
run_plug(plug);
}
/*
* our main entry point for writes from the rest of the FS.
*/
@ -1565,6 +1663,8 @@ int raid56_parity_write(struct btrfs_root *root, struct bio *bio,
u64 stripe_len)
{
struct btrfs_raid_bio *rbio;
struct btrfs_plug_cb *plug = NULL;
struct blk_plug_cb *cb;
rbio = alloc_rbio(root, bbio, raid_map, stripe_len);
if (IS_ERR(rbio)) {
@ -1574,7 +1674,27 @@ int raid56_parity_write(struct btrfs_root *root, struct bio *bio,
}
bio_list_add(&rbio->bio_list, bio);
rbio->bio_list_bytes = bio->bi_size;
return __raid56_parity_write(rbio);
/*
* don't plug on full rbios, just get them out the door
* as quickly as we can
*/
if (rbio_is_full(rbio))
return full_stripe_write(rbio);
cb = blk_check_plugged(btrfs_raid_unplug, root->fs_info,
sizeof(*plug));
if (cb) {
plug = container_of(cb, struct btrfs_plug_cb, cb);
if (!plug->info) {
plug->info = root->fs_info;
INIT_LIST_HEAD(&plug->rbio_list);
}
list_add_tail(&rbio->plug_list, &plug->rbio_list);
} else {
return __raid56_parity_write(rbio);
}
return 0;
}
/*