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[for-next,3/4] io_uring/rsrc: optimise single entry advance

Message ID aca3d68af0a5e1e463c95ceb2d98202b3eb57025.1677041932.git.asml.silence@gmail.com
State New
Headers
Series io_uring: registered huge buffer optimisations |

Commit Message

Pavel Begunkov Feb. 22, 2023, 2:36 p.m. UTC 
  Iterating within the first bvec entry should be essentially free, but we
use iov_iter_advance() for that, which shows up in benchmark profiles
taking up to 0.5% of CPU. Replace it with a hand coded version.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/rsrc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
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Patch

diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
index 53845e496881..ebbd2cea7582 100644
--- a/io_uring/rsrc.c
+++ b/io_uring/rsrc.c
@@ -1364,7 +1364,10 @@  int io_import_fixed(int ddir, struct iov_iter *iter,
 		const struct bio_vec *bvec = imu->bvec;
 
 		if (offset <= bvec->bv_len) {
-			iov_iter_advance(iter, offset);
+			iter->bvec = bvec;
+			iter->nr_segs = bvec->bv_len;
+			iter->count -= offset;
+			iter->iov_offset = offset;
 		} else {
 			unsigned long seg_skip;