Re: [PATCH] iov_iter: optimise iter type checking

On 06/12/2020 16:01, Pavel Begunkov wrote:

On 21/11/2020 14:37, Pavel Begunkov wrote:

quoted

The problem here is that iov_iter_is_*() helpers check types for
equality, but all iterate_* helpers do bitwise ands. This confuses
compilers, so even if some cases were handled separately with
iov_iter_is_*(), corresponding ifs in iterate*() right after are not
eliminated.

E.g. iov_iter_npages() first handles discards, but iterate_all_kinds()
still checks for discard iter type and generates unreachable code down
the line.

Ping. This one should be pretty simple

Ping please. Any doubts about this patch?

quoted

           text    data     bss     dec     hex filename
before:   24409     805       0   25214    627e lib/iov_iter.o
after:    23977     805       0   24782    60ce lib/iov_iter.o

Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 include/linux/uio.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 72d88566694e..c5970b2d3307 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h

@@ -57,27 +57,27 @@ static inline enum iter_type iov_iter_type(const struct iov_iter *i)
 
 static inline bool iter_is_iovec(const struct iov_iter *i)
 {
-	return iov_iter_type(i) == ITER_IOVEC;
+	return iov_iter_type(i) & ITER_IOVEC;
 }
 
 static inline bool iov_iter_is_kvec(const struct iov_iter *i)
 {
-	return iov_iter_type(i) == ITER_KVEC;
+	return iov_iter_type(i) & ITER_KVEC;
 }
 
 static inline bool iov_iter_is_bvec(const struct iov_iter *i)
 {
-	return iov_iter_type(i) == ITER_BVEC;
+	return iov_iter_type(i) & ITER_BVEC;
 }
 
 static inline bool iov_iter_is_pipe(const struct iov_iter *i)
 {
-	return iov_iter_type(i) == ITER_PIPE;
+	return iov_iter_type(i) & ITER_PIPE;
 }
 
 static inline bool iov_iter_is_discard(const struct iov_iter *i)
 {
-	return iov_iter_type(i) == ITER_DISCARD;
+	return iov_iter_type(i) & ITER_DISCARD;
 }
 
 static inline unsigned char iov_iter_rw(const struct iov_iter *i)

-- 
Pavel Begunkov