iov_iter: optimise bvec iov_iter_advance()

iov_iter_advance() is heavily used, but implemented through generic
means. For bvecs there is a specifically crafted function for that, so
use bvec_iter_advance() instead, it's faster and slimmer.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 6c597cd..e55357f 100644 (file)
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1065,6 +1065,21 @@ static void pipe_advance(struct iov_iter *i, size_t size)
        pipe_truncate(i);
 }
 
+static void iov_iter_bvec_advance(struct iov_iter *i, size_t size)
+{
+       struct bvec_iter bi;
+
+       bi.bi_size = i->count;
+       bi.bi_bvec_done = i->iov_offset;
+       bi.bi_idx = 0;
+       bvec_iter_advance(i->bvec, &bi, size);
+
+       i->bvec += bi.bi_idx;
+       i->nr_segs -= bi.bi_idx;
+       i->count = bi.bi_size;
+       i->iov_offset = bi.bi_bvec_done;
+}
+
 void iov_iter_advance(struct iov_iter *i, size_t size)
 {
        if (unlikely(iov_iter_is_pipe(i))) {
@@ -1075,6 +1090,10 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
                i->count -= size;
                return;
        }
+       if (iov_iter_is_bvec(i)) {
+               iov_iter_bvec_advance(i, size);
+               return;
+       }
        iterate_and_advance(i, size, v, 0, 0, 0)
 }
 EXPORT_SYMBOL(iov_iter_advance);