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>
diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 7ccddca..e34e568 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -97,9 +97,10 @@
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;
@@ -1558,6 +1559,103 @@
}
/*
+ * 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.
*/
int raid56_parity_write(struct btrfs_root *root, struct bio *bio,
@@ -1565,6 +1663,8 @@
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 @@
}
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;
}
/*