Re: [PATCH v1 09/15] io_uring/zcrx: add interface queue and refill queue

Jens Axboe
2024-10-09T17:51:00Z

On 10/7/24 4:15 PM, David Wei wrote:
> From: David Wei <davidhwei@meta.com>
>
> Add a new object called an interface queue (ifq) that represents a net rx queue
> that has been configured for zero copy. Each ifq is registered using a new
> registration opcode IORING_REGISTER_ZCRX_IFQ.
>
> The refill queue is allocated by the kernel and mapped by userspace using a new
> offset IORING_OFF_RQ_RING, in a similar fashion to the main SQ/CQ. It is used
> by userspace to return buffers that it is done with, which will then be re-used
> by the netdev again.
>
> The main CQ ring is used to notify userspace of received data by using the
> upper 16 bytes of a big CQE as a new struct io_uring_zcrx_cqe. Each entry
> contains the offset + len to the data.
>
> For now, each io_uring instance only has a single ifq.

Looks pretty straight forward to me, but please wrap your commit
messages at ~72 chars or it doesn't read so well in the git log.

A few minor comments...

> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> index adc2524fd8e3..567cdb89711e 100644
> --- a/include/uapi/linux/io_uring.h
> +++ b/include/uapi/linux/io_uring.h
> @@ -595,6 +597,9 @@ enum io_uring_register_op {
> IORING_REGISTER_NAPI = 27,
> IORING_UNREGISTER_NAPI = 28,
>
> + /* register a netdev hw rx queue for zerocopy */
> + IORING_REGISTER_ZCRX_IFQ = 29,
> +

Will need to change as the current tree has moved a bit beyond this. Not
a huge deal, just an FYI as it obviously impacts userspace too.

> +struct io_uring_zcrx_rqe {
> + __u64 off;
> + __u32 len;
> + __u32 __pad;
> +};
> +
> +struct io_uring_zcrx_cqe {
> + __u64 off;
> + __u64 __pad;
> +};

Would be nice to avoid padding for this one as it doubles its size. But
at the same time, always nice to have padding for future proofing...

Always a good idea to add padding, but

> diff --git a/io_uring/Makefile b/io_uring/Makefile
> index 61923e11c767..1a1184f3946a 100644
> --- a/io_uring/Makefile
> +++ b/io_uring/Makefile
> @@ -10,6 +10,7 @@ obj-$(CONFIG_IO_URING) += io_uring.o opdef.o kbuf.o rsrc.o notif.o \
> epoll.o statx.o timeout.o fdinfo.o \
> cancel.o waitid.o register.o \
> truncate.o memmap.o
> +obj-$(CONFIG_PAGE_POOL) += zcrx.o
> obj-$(CONFIG_IO_WQ) += io-wq.o
> obj-$(CONFIG_FUTEX) += futex.o
> obj-$(CONFIG_NET_RX_BUSY_POLL) += napi.o

I wonder if this should be expressed a bit differently. Probably have a
CONFIG_IO_URING_ZCRX which depends on CONFIG_INET and CONFIG_PAGE_POOL.
And then you can also use that rather than doing:

#if defined(CONFIG_PAGE_POOL) && defined(CONFIG_INET)

in some spots. Not a big deal, it'll work as-is. And honestly should
probably cleanup the existing IO_WQ symbol while at it, so perhaps
better left for after the fact.

> +static int io_allocate_rbuf_ring(struct io_zcrx_ifq *ifq,
> + struct io_uring_zcrx_ifq_reg *reg)
> +{
> + size_t off, size;
> + void *ptr;
> +
> + off = sizeof(struct io_uring);
> + size = off + sizeof(struct io_uring_zcrx_rqe) * reg->rq_entries;
> +
> + ptr = io_pages_map(&ifq->rqe_pages, &ifq->n_rqe_pages, size);
> + if (IS_ERR(ptr))
> + return PTR_ERR(ptr);
> +
> + ifq->rq_ring = (struct io_uring *)ptr;
> + ifq->rqes = (struct io_uring_zcrx_rqe *)((char *)ptr + off);
> + return 0;
> +}

No need to cast that ptr to char *.

Rest looks fine to me.

--
Jens Axboe