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authorChris Mason <chris.mason@oracle.com>2011-08-04 14:28:36 -0400
committerChris Mason <chris.mason@oracle.com>2011-08-05 13:48:18 -0400
commit2ab1ba68aeaecd41c4b34f0eaf1d70a37367fb1a (patch)
tree371f8ceacc858232947632eedbdb9cf9f049a8d0
parent0d10ee2e6deb5c8409ae65b970846344897d5e4e (diff)
Btrfs: force unplugs when switching from high to regular priority bios
Btrfs does bio submissions from a worker thread, and each device has a list of high priority bios and regular priority bios. Synchronous writes go to the high priority thread while async writes go to regular list. This commit brings back an explicit unplug any time we switch from high to regular priority, which makes it easier for the block layer to give us low latencies. Signed-off-by: Chris Mason <chris.mason@oracle.com>
-rw-r--r--fs/btrfs/volumes.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 53875ae73ad..3c5f2fcd82c 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -142,6 +142,7 @@ static noinline int run_scheduled_bios(struct btrfs_device *device)
unsigned long limit;
unsigned long last_waited = 0;
int force_reg = 0;
+ int sync_pending;
struct blk_plug plug;
/*
@@ -229,6 +230,22 @@ loop_lock:
BUG_ON(atomic_read(&cur->bi_cnt) == 0);
+ /*
+ * if we're doing the sync list, record that our
+ * plug has some sync requests on it
+ *
+ * If we're doing the regular list and there are
+ * sync requests sitting around, unplug before
+ * we add more
+ */
+ if (pending_bios == &device->pending_sync_bios) {
+ sync_pending = 1;
+ } else if (sync_pending) {
+ blk_finish_plug(&plug);
+ blk_start_plug(&plug);
+ sync_pending = 0;
+ }
+
submit_bio(cur->bi_rw, cur);
num_run++;
batch_run++;