[PATCH] Btrfs: remove batch plug in run_scheduled_IO

[PATCH] Btrfs: remove batch plug in run_scheduled_IO

[Liu Bo]

Block layer has a limit on plug, ie. BLK_MAX_REQUEST_COUNT == 16, so
we don't gain benefits by batching 64 bios here.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/btrfs/volumes.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e8b9a26..de55024 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -524,12 +524,6 @@ static noinline void run_scheduled_bios(struct btrfs_device *device)
 					 &device->work);
 			goto done;
 		}
-		/* unplug every 64 requests just for good measure */
-		if (batch_run % 64 == 0) {
-			blk_finish_plug(&plug);
-			blk_start_plug(&plug);
-			sync_pending = 0;
-		}
 	}
 
 	cond_resched();
-- 
2.9.4

Re: [PATCH] Btrfs: remove batch plug in run_scheduled_IO

[David Sterba]

On Fri, Sep 01, 2017 at 04:14:26PM -0600, Liu Bo wrote:
> Block layer has a limit on plug, ie. BLK_MAX_REQUEST_COUNT == 16, so
> we don't gain benefits by batching 64 bios here.

So this effectively does not change anything on the btrfs side, but we
can remove code that relies on some internal block layer behaviour.

Reviewed-by: David Sterba <dsterba@suse.com>