Subject: Re: [PATCH net-next v2 12/21] virtio_net: xsk: tx: support tx

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 9 Nov 2023 03:09:00 -0500

On Tue, Nov 07, 2023 at 11:12:18AM +0800, Xuan Zhuo wrote:
> The driver's tx napi is very important for XSK. It is responsible for
> obtaining data from the XSK queue and sending it out.
> 
> At the beginning, we need to trigger tx napi.
> 
> Signed-off-by: Xuan Zhuo <[email-masked]>
> ---
>  drivers/net/virtio/main.c       |  12 +++-
>  drivers/net/virtio/virtio_net.h |   3 +-
>  drivers/net/virtio/xsk.c        | 110 ++++++++++++++++++++++++++++++++
>  drivers/net/virtio/xsk.h        |  13 ++++
>  4 files changed, 136 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
> index 6c608b3ce27d..ff6bc764089d 100644
> --- a/drivers/net/virtio/main.c
> +++ b/drivers/net/virtio/main.c
> @@ -2074,6 +2074,7 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
>  	struct virtnet_info *vi = sq->vq->vdev->priv;
>  	unsigned int index = vq2txq(sq->vq);
>  	struct netdev_queue *txq;
> +	int busy = 0;
>  	int opaque;
>  	bool done;
>  
> @@ -2086,11 +2087,20 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
>  	txq = netdev_get_tx_queue(vi->dev, index);
>  	__netif_tx_lock(txq, raw_smp_processor_id());
>  	virtqueue_disable_cb(sq->vq);
> -	free_old_xmit(sq, true);
> +
> +	if (sq->xsk.pool)
> +		busy |= virtnet_xsk_xmit(sq, sq->xsk.pool, budget);

You use bitwise or on errno values? What's going on here?

> +	else
> +		free_old_xmit(sq, true);
>  
>  	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
>  		netif_tx_wake_queue(txq);
>  
> +	if (busy) {
> +		__netif_tx_unlock(txq);
> +		return budget;
> +	}
> +
>  	opaque = virtqueue_enable_cb_prepare(sq->vq);
>  
>  	done = napi_complete_done(napi, 0);
> diff --git a/drivers/net/virtio/virtio_net.h b/drivers/net/virtio/virtio_net.h
> index 442af4673bf8..1c21af47e13c 100644
> --- a/drivers/net/virtio/virtio_net.h
> +++ b/drivers/net/virtio/virtio_net.h
> @@ -9,7 +9,8 @@
>  #include <net/xdp_sock_drv.h>
>  
>  #define VIRTIO_XDP_FLAG	BIT(0)
> -#define VIRTIO_XMIT_DATA_MASK (VIRTIO_XDP_FLAG)
> +#define VIRTIO_XSK_FLAG	BIT(1)
> +#define VIRTIO_XMIT_DATA_MASK (VIRTIO_XDP_FLAG | VIRTIO_XSK_FLAG)
>  
>  /* RX packet size EWMA. The average packet size is used to determine the packet
>   * buffer size when refilling RX rings. As the entire RX ring may be refilled
> diff --git a/drivers/net/virtio/xsk.c b/drivers/net/virtio/xsk.c
> index 8b397787603f..caa448308232 100644
> --- a/drivers/net/virtio/xsk.c
> +++ b/drivers/net/virtio/xsk.c
> @@ -4,9 +4,119 @@
>   */
>  
>  #include "virtio_net.h"
> +#include "xsk.h"
>  
>  static struct virtio_net_hdr_mrg_rxbuf xsk_hdr;
>  
> +static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
> +{
> +	sg->dma_address = addr;
> +	sg->length = len;
> +}
> +
> +static void virtnet_xsk_check_queue(struct virtnet_sq *sq)
> +{
> +	struct virtnet_info *vi = sq->vq->vdev->priv;
> +	struct net_device *dev = vi->dev;
> +	int qnum = sq - vi->sq;
> +
> +	/* If it is a raw buffer queue, it does not check whether the status
> +	 * of the queue is stopped when sending. So there is no need to check
> +	 * the situation of the raw buffer queue.
> +	 */
> +	if (virtnet_is_xdp_raw_buffer_queue(vi, qnum))
> +		return;
> +
> +	/* If this sq is not the exclusive queue of the current cpu,
> +	 * then it may be called by start_xmit, so check it running out
> +	 * of space.
> +	 *
> +	 * Stop the queue to avoid getting packets that we are
> +	 * then unable to transmit. Then wait the tx interrupt.
> +	 */
> +	if (sq->vq->num_free < 2 + MAX_SKB_FRAGS)

what does MAX_SKB_FRAGS have to do with it? And where's 2 coming from?

> +		netif_stop_subqueue(dev, qnum);
> +}
> +
> +static int virtnet_xsk_xmit_one(struct virtnet_sq *sq,
> +				struct xsk_buff_pool *pool,
> +				struct xdp_desc *desc)
> +{
> +	struct virtnet_info *vi;
> +	dma_addr_t addr;
> +
> +	vi = sq->vq->vdev->priv;
> +
> +	addr = xsk_buff_raw_get_dma(pool, desc->addr);
> +	xsk_buff_raw_dma_sync_for_device(pool, addr, desc->len);
> +
> +	sg_init_table(sq->sg, 2);
> +
> +	sg_fill_dma(sq->sg, sq->xsk.hdr_dma_address, vi->hdr_len);
> +	sg_fill_dma(sq->sg + 1, addr, desc->len);
> +
> +	return virtqueue_add_outbuf(sq->vq, sq->sg, 2,
> +				    virtnet_xsk_to_ptr(desc->len), GFP_ATOMIC);
> +}
> +
> +static int virtnet_xsk_xmit_batch(struct virtnet_sq *sq,
> +				  struct xsk_buff_pool *pool,
> +				  unsigned int budget,
> +				  u64 *kicks)
> +{
> +	struct xdp_desc *descs = pool->tx_descs;
> +	u32 nb_pkts, max_pkts, i;
> +	bool kick = false;
> +	int err;
> +
> +	/* Every xsk tx packet needs two desc(virtnet header and packet). So we
> +	 * use sq->vq->num_free / 2 as the limitation.
> +	 */
> +	max_pkts = min_t(u32, budget, sq->vq->num_free / 2);
> +
> +	nb_pkts = xsk_tx_peek_release_desc_batch(pool, max_pkts);
> +	if (!nb_pkts)
> +		return 0;
> +
> +	for (i = 0; i < nb_pkts; i++) {
> +		err = virtnet_xsk_xmit_one(sq, pool, &descs[i]);
> +		if (unlikely(err))
> +			break;
> +
> +		kick = true;
> +	}
> +
> +	if (kick && virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq))
> +		(*kicks)++;
> +
> +	return i;
> +}
> +
> +bool virtnet_xsk_xmit(struct virtnet_sq *sq, struct xsk_buff_pool *pool,
> +		      int budget)
> +{
> +	u64 bytes = 0, packets = 0, kicks = 0;
> +	int sent;
> +
> +	virtnet_free_old_xmit(sq, true, &bytes, &packets);
> +
> +	sent = virtnet_xsk_xmit_batch(sq, pool, budget, &kicks);
> +
> +	virtnet_xsk_check_queue(sq);
> +
> +	u64_stats_update_begin(&sq->stats.syncp);
> +	u64_stats_add(&sq->stats.packets, packets);
> +	u64_stats_add(&sq->stats.bytes, bytes);
> +	u64_stats_add(&sq->stats.kicks, kicks);
> +	u64_stats_add(&sq->stats.xdp_tx,  sent);
> +	u64_stats_update_end(&sq->stats.syncp);
> +
> +	if (xsk_uses_need_wakeup(pool))
> +		xsk_set_tx_need_wakeup(pool);
> +
> +	return sent == budget;
> +}
> +
>  static int virtnet_rq_bind_xsk_pool(struct virtnet_info *vi, struct virtnet_rq *rq,
>  				    struct xsk_buff_pool *pool)
>  {
> diff --git a/drivers/net/virtio/xsk.h b/drivers/net/virtio/xsk.h
> index 1918285c310c..73ca8cd5308b 100644
> --- a/drivers/net/virtio/xsk.h
> +++ b/drivers/net/virtio/xsk.h
> @@ -3,5 +3,18 @@
>  #ifndef __XSK_H__
>  #define __XSK_H__
>  
> +#define VIRTIO_XSK_FLAG_OFFSET	4
> +
> +static inline void *virtnet_xsk_to_ptr(u32 len)
> +{
> +	unsigned long p;
> +
> +	p = len << VIRTIO_XSK_FLAG_OFFSET;
> +
> +	return (void *)(p | VIRTIO_XSK_FLAG);
> +}
> +
>  int virtnet_xsk_pool_setup(struct net_device *dev, struct netdev_bpf *xdp);
> +bool virtnet_xsk_xmit(struct virtnet_sq *sq, struct xsk_buff_pool *pool,
> +		      int budget);
>  #endif
> -- 
> 2.32.0.3.g01195cf9f