Commit 7a1bcb5d authored by Al Viro's avatar Al Viro
Browse files

iov_iter: massage iterate_iovec and iterate_kvec to logics similar to iterate_bvec 



Premature optimization is the root of all evil...  Trying
to unroll the first pass through the loop makes it harder
to follow and not just for readers - compiler ends up
generating worse code than it would on a "non-optimized"
loop.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent f5da8354

lib/iov_iter.c

+36 −55
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
	size_t left;						\

	size_t wanted = n;					\

	__p = i->iov;						\

	do {							\

		__v.iov_len = min(n, __p->iov_len - skip);	\

		if (likely(__v.iov_len)) {			\

			__v.iov_base = __p->iov_base + skip;	\
@@ -27,44 +28,32 @@ 
			__v.iov_len -= left;			\

			skip += __v.iov_len;			\

			n -= __v.iov_len;			\

	} else {					\

		left = 0;				\

			if (skip < __p->iov_len)		\

				break;				\

		}						\

	while (unlikely(!left && n)) {			\

		__p++;						\

		__v.iov_len = min(n, __p->iov_len);	\

		if (unlikely(!__v.iov_len))		\

			continue;			\

		__v.iov_base = __p->iov_base;		\

		left = (STEP);				\

		__v.iov_len -= left;			\

		skip = __v.iov_len;			\

		n -= __v.iov_len;			\

	}						\

		skip = 0;					\

	} while (n);						\

	n = wanted - n;						\

}



#define iterate_kvec(i, n, __v, __p, skip, STEP) {		\

	size_t wanted = n;					\

	__p = i->kvec;						\

	do {							\

		__v.iov_len = min(n, __p->iov_len - skip);	\

		if (likely(__v.iov_len)) {			\

			__v.iov_base = __p->iov_base + skip;	\

			(void)(STEP);				\

			skip += __v.iov_len;			\

			n -= __v.iov_len;			\

			if (skip < __p->iov_len)		\

				break;				\

		}						\

	while (unlikely(n)) {				\

		__p++;						\

		__v.iov_len = min(n, __p->iov_len);	\

		if (unlikely(!__v.iov_len))		\

			continue;			\

		__v.iov_base = __p->iov_base;		\

		(void)(STEP);				\

		skip = __v.iov_len;			\

		n -= __v.iov_len;			\

	}						\

	n = wanted;					\

		skip = 0;					\

	} while (n);						\

	n = wanted - n;						\

}



#define iterate_bvec(i, n, __v, __bi, skip, STEP) {	\
@@ -123,10 +112,6 @@ 
			const struct iovec *iov;		\

			struct iovec v;				\

			iterate_iovec(i, n, v, iov, skip, (I))	\

			if (skip == iov->iov_len) {		\

				iov++;				\

				skip = 0;			\

			}					\

			i->nr_segs -= iov - i->iov;		\

			i->iov = iov;				\

		} else if (iov_iter_is_bvec(i)) {		\
@@ -141,10 +126,6 @@ 
			const struct kvec *kvec;		\

			struct kvec v;				\

			iterate_kvec(i, n, v, kvec, skip, (K))	\

			if (skip == kvec->iov_len) {		\

				kvec++;				\

				skip = 0;			\

			}					\

			i->nr_segs -= kvec - i->kvec;		\

			i->kvec = kvec;				\

		} else if (iov_iter_is_xarray(i)) {		\