Btrfs: run the backing dev more often in the submit_bio helper

The submit_bio helper thread can decide to loop back around to
service more bios.  This commit forces it to unplug first, which helps
reduce the latency seen by submitters.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 10 insertions, 10 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 41ecbb2347f2..ace2e8d7bbcd 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -325,16 +325,6 @@ loop_lock:
                 num_sync_run = 0;
                 blk_run_backing_dev(bdi, NULL);
         }
-
-        cond_resched();
-        if (again)
-                goto loop;
-
-        spin_lock(&device->io_lock);
-        if (device->pending_bios.head || device->pending_sync_bios.head)
-                goto loop_lock;
-        spin_unlock(&device->io_lock);
-
         /*
          * IO has already been through a long path to get here.  Checksumming,
          * async helper threads, perhaps compression.  We've done a pretty
@@ -346,6 +336,16 @@ loop_lock:
          * cared about found its way down here.
          */
         blk_run_backing_dev(bdi, NULL);
+
+        cond_resched();
+        if (again)
+                goto loop;
+
+        spin_lock(&device->io_lock);
+        if (device->pending_bios.head || device->pending_sync_bios.head)
+                goto loop_lock;
+        spin_unlock(&device->io_lock);
+
 done:
         return 0;
 }