dm: avoid indirect call in __dm_make_request

Indirect calls are inefficient because of retpolines that are used for
spectre workaround. This patch replaces an indirect call with a condition
(that can be predicted by the branch predictor).

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index dddbca63e140e82c6110b8e8b92a2697a7cc25a0..fa70c90e67574115831f17b1db3377bea147c2ba 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1696,10 +1696,7 @@ out:
        return ret;
 }
 
-typedef blk_qc_t (process_bio_fn)(struct mapped_device *, struct dm_table *, struct bio *);
-
-static blk_qc_t __dm_make_request(struct request_queue *q, struct bio *bio,
-                                 process_bio_fn process_bio)
+static blk_qc_t dm_make_request(struct request_queue *q, struct bio *bio)
 {
        struct mapped_device *md = q->queuedata;
        blk_qc_t ret = BLK_QC_T_NONE;
@@ -1719,26 +1716,15 @@ static blk_qc_t __dm_make_request(struct request_queue *q, struct bio *bio,
                return ret;
        }
 
-       ret = process_bio(md, map, bio);
+       if (dm_get_md_type(md) == DM_TYPE_NVME_BIO_BASED)
+               ret = __process_bio(md, map, bio);
+       else
+               ret = __split_and_process_bio(md, map, bio);
 
        dm_put_live_table(md, srcu_idx);
        return ret;
 }
 
-/*
- * The request function that remaps the bio to one target and
- * splits off any remainder.
- */
-static blk_qc_t dm_make_request(struct request_queue *q, struct bio *bio)
-{
-       return __dm_make_request(q, bio, __split_and_process_bio);
-}
-
-static blk_qc_t dm_make_request_nvme(struct request_queue *q, struct bio *bio)
-{
-       return __dm_make_request(q, bio, __process_bio);
-}
-
 static int dm_any_congested(void *congested_data, int bdi_bits)
 {
        int r = bdi_bits;
@@ -2229,12 +2215,9 @@ int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
                break;
        case DM_TYPE_BIO_BASED:
        case DM_TYPE_DAX_BIO_BASED:
-               dm_init_normal_md_queue(md);
-               blk_queue_make_request(md->queue, dm_make_request);
-               break;
        case DM_TYPE_NVME_BIO_BASED:
                dm_init_normal_md_queue(md);
-               blk_queue_make_request(md->queue, dm_make_request_nvme);
+               blk_queue_make_request(md->queue, dm_make_request);
                break;
        case DM_TYPE_NONE:
                WARN_ON_ONCE(true);