block: fix DISCARD_BARRIER requests

Filesystems assume that DISCARD_BARRIER are full barriers, so that they
don't have to track in-progress discard operation when submitting new I/O.
But currently we only treat them as elevator barriers, which don't
actually do the nessecary queue drains.

Also remove the unlikely around both the DISCARD and BARRIER requests -
the happen far too often for a static mispredict.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/block/blk-core.c b/block/blk-core.c
index f84cce4..3deca77 100644 (file)
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1149,13 +1149,10 @@ void init_request_from_bio(struct request *req, struct bio *bio)
        else
                req->cmd_flags |= bio->bi_rw & REQ_FAILFAST_MASK;
 
-       if (unlikely(bio_rw_flagged(bio, BIO_RW_DISCARD))) {
+       if (bio_rw_flagged(bio, BIO_RW_DISCARD))
                req->cmd_flags |= REQ_DISCARD;
-               if (bio_rw_flagged(bio, BIO_RW_BARRIER))
-                       req->cmd_flags |= REQ_SOFTBARRIER;
-       } else if (unlikely(bio_rw_flagged(bio, BIO_RW_BARRIER)))
+       if (bio_rw_flagged(bio, BIO_RW_BARRIER))
                req->cmd_flags |= REQ_HARDBARRIER;
-
        if (bio_rw_flagged(bio, BIO_RW_SYNCIO))
                req->cmd_flags |= REQ_RW_SYNC;
        if (bio_rw_flagged(bio, BIO_RW_META))