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@xxxxxxxxxx>
---
drivers/md/dm.c | 27 ++++++---------------------
1 file changed, 6 insertions(+), 21 deletions(-)
Index: linux-2.6/drivers/md/dm.c
===================================================================
--- linux-2.6.orig/drivers/md/dm.c 2018-10-16 23:19:49.900000000 +0200
+++ linux-2.6/drivers/md/dm.c 2018-10-16 23:19:51.000000000 +0200
@@ -1687,8 +1687,7 @@ out:
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;
@@ -1708,26 +1707,15 @@ static blk_qc_t __dm_make_request(struct
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;
@@ -2235,12 +2223,9 @@ int dm_setup_md_queue(struct mapped_devi
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);
--
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