Re: [PATCHv10 6/9] io_uring: enable per-io hinting capability

[Jens Axboe <axboe@kernel.dk>]

On 10/29/24 9:19 AM, Keith Busch wrote:
> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index 0247452837830..6e1985d3b306c 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -92,6 +92,10 @@ struct io_uring_sqe {
>  			__u16	addr_len;
>  			__u16	__pad3[1];
>  		};
> +		struct {
> +			__u16	write_hint;
> +			__u16	__pad4[1];
> +		};

Might make more sense to have this overlap further down, with the
passthrough command. That'd put it solidly out of anything that isn't
passthrough or needs addr3.

> diff --git a/io_uring/rw.c b/io_uring/rw.c
> index 7ce1cbc048faf..b5dea58356d93 100644
> --- a/io_uring/rw.c
> +++ b/io_uring/rw.c
> @@ -279,7 +279,8 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
>  		rw->kiocb.ki_ioprio = get_current_ioprio();
>  	}
>  	rw->kiocb.dio_complete = NULL;
> -
> +	if (ddir == ITER_SOURCE)
> +		rw->kiocb.ki_write_hint = READ_ONCE(sqe->write_hint);
>  	rw->addr = READ_ONCE(sqe->addr);
>  	rw->len = READ_ONCE(sqe->len);
>  	rw->flags = READ_ONCE(sqe->rw_flags);

Can't we just read it unconditionally? I know it's a write hint, hence
why checking for ITER_SOURCE, but if we can just set it regardless, then
we don't need to branch around that.

-- 
Jens Axboe