From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mikulas Patocka Subject: [patch 1/5] dm: avoid indirect call in __dm_make_request Date: Tue, 06 Nov 2018 22:34:59 +0100 Message-ID: <20181106213853.335317680@debian-a64.vm> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline; filename=dm-avoid-indirect-call.patch List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mike Snitzer , "Alasdair G. Kergon" Cc: dm-devel@redhat.com, Mikulas Patocka List-Id: dm-devel.ids 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 --- 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);