Because of how for_each_bvec() works it never advances across multiple
entries at a time, so bvec_iter_advance() is an overkill. Add
specialised bvec_iter_advance_single() that is faster. It also handles
zero-len bvecs, so can kill bvec_iter_skip_zero_bvec().
text data bss dec hex filename
before:
23977 805 0 24782 60ce lib/iov_iter.o
before, bvec_iter_advance() w/o WARN_ONCE()
22886 600 0 23486 5bbe ./lib/iov_iter.o
after:
21862 600 0 22462 57be lib/iov_iter.o
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
include/linux/bvec.h | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index 2efec10bf792..ff832e698efb 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -121,18 +121,28 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
return true;
}
-static inline void bvec_iter_skip_zero_bvec(struct bvec_iter *iter)
+/*
+ * A simpler version of bvec_iter_advance(), @bytes should not span
+ * across multiple bvec entries, i.e. bytes <= bv[i->bi_idx].bv_len
+ */
+static inline void bvec_iter_advance_single(const struct bio_vec *bv,
+ struct bvec_iter *iter, unsigned int bytes)
{
- iter->bi_bvec_done = 0;
- iter->bi_idx++;
+ unsigned int done = iter->bi_bvec_done + bytes;
+
+ if (done == bv[iter->bi_idx].bv_len) {
+ done = 0;
+ iter->bi_idx++;
+ }
+ iter->bi_bvec_done = done;
+ iter->bi_size -= bytes;
}
#define for_each_bvec(bvl, bio_vec, iter, start) \
for (iter = (start); \
(iter).bi_size && \
((bvl = bvec_iter_bvec((bio_vec), (iter))), 1); \
- (bvl).bv_len ? (void)bvec_iter_advance((bio_vec), &(iter), \
- (bvl).bv_len) : bvec_iter_skip_zero_bvec(&(iter)))
+ bvec_iter_advance_single((bio_vec), &(iter), (bvl).bv_len))
/* for iterating one bio from start to end */
#define BVEC_ITER_ALL_INIT (struct bvec_iter) \
--
2.24.0
