diff options
author | Pavel Begunkov | 2019-11-30 23:23:52 +0300 |
---|---|---|
committer | Jens Axboe | 2019-12-03 07:36:38 -0700 |
commit | 795ee49c1a28d1b3eeb2b463f18d557700fc6153 (patch) | |
tree | 37a0074d7559534cd68eb5d58883f5ab27f3bf7d | |
parent | 8cdda87a4414092cd210e766189cf0353a844861 (diff) |
block: optimise bvec_iter_advance()
bvec_iter_advance() is quite popular, but compilers fail to do proper
alias analysis and optimise it good enough. The assembly is checked
for gcc 9.2, x86-64.
- remove @iter->bi_size from min(...), as it's always less than @bytes.
Modify at the beginning and forget about it.
- the compiler isn't able to collapse memory dependencies and remove
writes in the loop. Help it by explicitely using local vars.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r-- | include/linux/bvec.h | 22 |
1 files changed, 10 insertions, 12 deletions
diff --git a/include/linux/bvec.h b/include/linux/bvec.h index a032f01e928c..679a42253170 100644 --- a/include/linux/bvec.h +++ b/include/linux/bvec.h @@ -87,26 +87,24 @@ struct bvec_iter_all { static inline bool bvec_iter_advance(const struct bio_vec *bv, struct bvec_iter *iter, unsigned bytes) { + unsigned int idx = iter->bi_idx; + if (WARN_ONCE(bytes > iter->bi_size, "Attempted to advance past end of bvec iter\n")) { iter->bi_size = 0; return false; } - while (bytes) { - const struct bio_vec *cur = bv + iter->bi_idx; - unsigned len = min3(bytes, iter->bi_size, - cur->bv_len - iter->bi_bvec_done); - - bytes -= len; - iter->bi_size -= len; - iter->bi_bvec_done += len; + iter->bi_size -= bytes; + bytes += iter->bi_bvec_done; - if (iter->bi_bvec_done == cur->bv_len) { - iter->bi_bvec_done = 0; - iter->bi_idx++; - } + while (bytes && bytes >= bv[idx].bv_len) { + bytes -= bv[idx].bv_len; + idx++; } + + iter->bi_idx = idx; + iter->bi_bvec_done = bytes; return true; } |