From 7ed4aab1381f3439f45032eb860f89d9da5e45c2 Mon Sep 17 00:00:00 2001 From: Steven Feng Date: Sat, 6 Jun 2026 10:42:18 +0800 Subject: [PATCH] block: optimize I/O merge hot path with unlikely() hints Remove redundant '== false' comparisons and add unlikely() branch prediction hints in block I/O merge path functions. These functions (ll_new_hw_segment, ll_merge_requests_fn, and blk_rq_merge_ok) are executed on every I/O request merge attempt, making them critical hot paths. Data integrity check failures are rare events, so marking these conditions as unlikely() helps the CPU optimize the common case by improving branch prediction. Changes: - Replace 'func() == false' with 'unlikely(!func())' for better code style and branch prediction This micro-optimization reduces branch misprediction penalties in high-frequency I/O merge paths. Signed-off-by: Steven Feng Link: https://patch.msgid.link/tencent_79B652BD0CC23E093F27914380F161E7E505@qq.com Signed-off-by: Jens Axboe --- block/blk-merge.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/block/blk-merge.c b/block/blk-merge.c index 7cc82a7a6f4e..ee1d9213f43e 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -545,7 +545,7 @@ static inline int ll_new_hw_segment(struct request *req, struct bio *bio, if (!blk_cgroup_mergeable(req, bio)) goto no_merge; - if (blk_integrity_merge_bio(req->q, req, bio) == false) + if (unlikely(!blk_integrity_merge_bio(req->q, req, bio))) goto no_merge; /* discard request merge won't add new segment */ @@ -647,7 +647,7 @@ static int ll_merge_requests_fn(struct request_queue *q, struct request *req, if (!blk_cgroup_mergeable(req, next->bio)) return 0; - if (blk_integrity_merge_rq(q, req, next) == false) + if (unlikely(!blk_integrity_merge_rq(q, req, next))) return 0; if (!bio_crypt_ctx_merge_rq(req, next)) @@ -903,7 +903,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio) if (!blk_cgroup_mergeable(rq, bio)) return false; - if (blk_integrity_merge_bio(rq->q, rq, bio) == false) + if (unlikely(!blk_integrity_merge_bio(rq->q, rq, bio))) return false; if (!bio_crypt_rq_ctx_compatible(rq, bio)) return false; @@ -913,7 +913,7 @@ bool blk_rq_merge_ok(struct request *rq, struct bio *bio) return false; if (rq->bio->bi_ioprio != bio->bi_ioprio) return false; - if (blk_atomic_write_mergeable_rq_bio(rq, bio) == false) + if (unlikely(!blk_atomic_write_mergeable_rq_bio(rq, bio))) return false; return true;