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 06:58:48 -0500

On Thu, Nov 09, 2023 at 07:06:23PM +0800, Xuan Zhuo wrote:
> On Thu, 9 Nov 2023 03:09:00 -0500, "Michael S. Tsirkin" <[email-masked]> wrote:
> > 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?
> 
> virtnet_xsk_xmit() return that it is busy or not. Not the errno.
> Here just record whether this handler is busy or not.

Ah I see it's a bool. So make busy a bool too.

> >
> >
> > > +	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?
> 
> check_sq_full_and_disable()
> 
> Thanks.

This is one example of duplication I was talking about earlier.

> >
> > > +		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
> >