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Commit 24113d48 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer
Browse files

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: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent cd19181b

drivers/md/dm.c

+6 −23
Original line number Diff line number Diff line
@@ -1696,10 +1696,7 @@ static blk_qc_t __process_bio(struct mapped_device *md, 
	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);