linux-kernel - Re: [PATCH] xsk: add cq event

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Date:   Mon, 16 Nov 2020 12:13:21 +0300
From:   Denis Kirjanov <kda@...ux-powerpc.org>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     netdev@...r.kernel.org,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xsk: add cq event

On 11/16/20, Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
> When we write all cq items to tx, we have to wait for a new event based
> on poll to indicate that it is writable. But the current writability is
> triggered based on whether tx is full or not, and In fact, when tx is
> dissatisfied, the user of cq's item may not necessarily get it, because it
> may still be occupied by the network card. In this case, we need to know
> when cq is available, so this patch adds a socket option, When the user
> configures this option using setsockopt, when cq is available, a
> readable event is generated for all xsk bound to this umem.
>
> I can't find a better description of this event,
> I think it can also be 'readable', although it is indeed different from
> the 'readable' of the new data. But the overhead of xsk checking whether
> cq or rx is readable is small.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  include/net/xdp_sock.h      |  1 +
>  include/uapi/linux/if_xdp.h |  1 +
>  net/xdp/xsk.c               | 28 ++++++++++++++++++++++++++++
>  3 files changed, 30 insertions(+)
>
> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> index 1a9559c..faf5b1a 100644
> --- a/include/net/xdp_sock.h
> +++ b/include/net/xdp_sock.h
> @@ -49,6 +49,7 @@ struct xdp_sock {
>  	struct xsk_buff_pool *pool;
>  	u16 queue_id;
>  	bool zc;
> +	bool cq_event;
>  	enum {
>  		XSK_READY = 0,
>  		XSK_BOUND,
> diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
> index a78a809..2dba3cb 100644
> --- a/include/uapi/linux/if_xdp.h
> +++ b/include/uapi/linux/if_xdp.h
> @@ -63,6 +63,7 @@ struct xdp_mmap_offsets {
>  #define XDP_UMEM_COMPLETION_RING	6
>  #define XDP_STATISTICS			7
>  #define XDP_OPTIONS			8
> +#define XDP_CQ_EVENT			9
>
>  struct xdp_umem_reg {
>  	__u64 addr; /* Start of packet data area */
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index cfbec39..0c53403 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -285,7 +285,16 @@ void __xsk_map_flush(void)
>
>  void xsk_tx_completed(struct xsk_buff_pool *pool, u32 nb_entries)
>  {
> +	struct xdp_sock *xs;
> +
>  	xskq_prod_submit_n(pool->cq, nb_entries);
> +
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(xs, &pool->xsk_tx_list, tx_list) {
> +		if (xs->cq_event)
> +			sock_def_readable(&xs->sk);
> +	}
> +	rcu_read_unlock();
>  }
>  EXPORT_SYMBOL(xsk_tx_completed);
>
> @@ -495,6 +504,9 @@ static __poll_t xsk_poll(struct file *file, struct
> socket *sock,
>  			__xsk_sendmsg(sk);
>  	}
>
> +	if (xs->cq_event && pool->cq && !xskq_prod_is_empty(pool->cq))
> +		mask |= EPOLLIN | EPOLLRDNORM;
> +
>  	if (xs->rx && !xskq_prod_is_empty(xs->rx))
>  		mask |= EPOLLIN | EPOLLRDNORM;
>  	if (xs->tx && !xskq_cons_is_full(xs->tx))
> @@ -882,6 +894,22 @@ static int xsk_setsockopt(struct socket *sock, int
> level, int optname,
>  		mutex_unlock(&xs->mutex);
>  		return err;
>  	}
> +	case XDP_CQ_EVENT:
> +	{
> +		int cq_event;
> +
> +		if (optlen < sizeof(cq_event))
> +			return -EINVAL;
> +		if (copy_from_sockptr(&cq_event, optval, sizeof(cq_event)))
> +			return -EFAULT;
> +
> +		if (cq_event)
> +			xs->cq_event = true;
> +		else
> +			xs->cq_event = false;

It's false by default, isn't it?

> +
> +		return 0;
> +	}
>  	default:
>  		break;
>  	}
> --
> 1.8.3.1
>
>