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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>
This commit is contained in:
Mikulas Patocka 2018-11-06 22:34:59 +01:00 committed by Mike Snitzer
parent cd19181bf9
commit 24113d4878
1 changed files with 6 additions and 23 deletions
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29
drivers/md/dm.c
View File

@ -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);