Re: [PATCH] iov_iter: optimise iter type checking

Pavel Begunkov
2020-12-06T16:05:18Z

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

>
> 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