netdev - Re: [PATCH net-next v2 6/7] virtio-net, xsk: implement xsk wakeup callback

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Date:   Tue, 19 Jan 2021 12:50:25 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next v2 6/7] virtio-net, xsk: implement xsk wakeup
 callback


On 2021/1/16 上午10:59, Xuan Zhuo wrote:
> Since I did not find an interface to directly notify virtio to generate
> a tx interrupt, I sent some data to trigger a new tx interrupt.
>
> Another advantage of this is that the transmission delay will be
> relatively small, and there is no need to wait for the tx interrupt to
> start softirq.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>   drivers/net/virtio_net.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 51 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 42aa9ad..e552c2d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2841,6 +2841,56 @@ static int virtnet_xsk_run(struct send_queue *sq,
>   	return ret;
>   }
>   
> +static int virtnet_xsk_wakeup(struct net_device *dev, u32 qid, u32 flag)
> +{
> +	struct virtnet_info *vi = netdev_priv(dev);
> +	struct send_queue *sq;
> +	struct xsk_buff_pool *pool;
> +	struct netdev_queue *txq;
> +
> +	if (!netif_running(dev))
> +		return -ENETDOWN;
> +
> +	if (qid >= vi->curr_queue_pairs)
> +		return -EINVAL;
> +
> +	sq = &vi->sq[qid];
> +
> +	rcu_read_lock();
> +
> +	pool = rcu_dereference(sq->xsk.pool);
> +	if (!pool)
> +		goto end;
> +
> +	if (test_and_set_bit(VIRTNET_STATE_XSK_WAKEUP, &sq->xsk.state))
> +		goto end;
> +
> +	txq = netdev_get_tx_queue(dev, qid);
> +
> +	local_bh_disable();
> +	__netif_tx_lock(txq, raw_smp_processor_id());


You can use __netif_tx_lock_bh().

Thanks


> +
> +	/* Send part of the package directly to reduce the delay in sending the
> +	 * package, and this can actively trigger the tx interrupts.
> +	 *
> +	 * If the package is not processed, then continue processing in the
> +	 * subsequent tx interrupt(virtnet_poll_tx).
> +	 *
> +	 * If no packet is sent out, the ring of the device is full. In this
> +	 * case, we will still get a tx interrupt response. Then we will deal
> +	 * with the subsequent packet sending work.
> +	 */
> +
> +	virtnet_xsk_run(sq, pool, xsk_budget);
> +
> +	__netif_tx_unlock(txq);
> +	local_bh_enable();
> +
> +end:
> +	rcu_read_unlock();
> +	return 0;
> +}
> +
>   static int virtnet_get_phys_port_name(struct net_device *dev, char *buf,
>   				      size_t len)
>   {
> @@ -2895,6 +2945,7 @@ static int virtnet_set_features(struct net_device *dev,
>   	.ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
>   	.ndo_bpf		= virtnet_xdp,
>   	.ndo_xdp_xmit		= virtnet_xdp_xmit,
> +	.ndo_xsk_wakeup		= virtnet_xsk_wakeup,
>   	.ndo_features_check	= passthru_features_check,
>   	.ndo_get_phys_port_name	= virtnet_get_phys_port_name,
>   	.ndo_set_features	= virtnet_set_features,