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Re: [PATCH v3] Use io_uring_register_ring_fd() to skip fd operations
From: |
Fam Zheng |
Subject: |
Re: [PATCH v3] Use io_uring_register_ring_fd() to skip fd operations |
Date: |
Thu, 21 Apr 2022 14:36:00 +0100 |
On 2022-04-19 07:33, Sam Li wrote:
> Linux recently added a new io_uring(7) optimization API that QEMU
> doesn't take advantage of yet. The liburing library that QEMU uses
> has added a corresponding new API calling io_uring_register_ring_fd().
> When this API is called after creating the ring, the io_uring_submit()
> library function passes a flag to the io_uring_enter(2) syscall
> allowing it to skip the ring file descriptor fdget()/fdput()
> operations. This saves some CPU cycles.
>
> Signed-off-by: Sam Li <faithilikerun@gmail.com>
> ---
> block/io_uring.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/block/io_uring.c b/block/io_uring.c
> index 782afdb433..51f4834b69 100644
> --- a/block/io_uring.c
> +++ b/block/io_uring.c
> @@ -435,8 +435,16 @@ LuringState *luring_init(Error **errp)
> }
>
> ioq_init(&s->io_q);
> - return s;
> + if (io_uring_register_ring_fd(&s->ring) < 0) {
> + /*
> + * Only warn about this error: we will fallback to the non-optimized
> + * io_uring operations.
> + */
> + error_setg_errno(errp, errno,
> + "failed to register linux io_uring ring file
> descriptor");
> + }
>
> + return s;
As a general convention, I don't think the errp is going to get proper handling
by the callers, if non-NULL is returned like here. IOW a matching error_free is
never called and this is memory leak?
I guess error_report is better?
Fam
> }
>
> void luring_cleanup(LuringState *s)
> --
> 2.35.1
>
>