Re: [PATCH net-next v3 8/8] virtio-net: free old xmit handle xsk

[Jason Wang <jasowang@redhat.com>]

在 2021/3/31 下午3:11, Xuan Zhuo 写道:
> Based on the last two bit of ptr returned by virtqueue_get_buf, 01
> represents the packet sent by xdp, 10 is the packet sent by xsk, and 00
> is skb by default.
>
> If the xmit work of xsk has not been completed, but the ring is full,
> napi must first exit and wait for the ring to be available, so
> need_wakeup is set. If __free_old_xmit is called first by start_xmit, we
> can quickly wake up napi to execute xsk xmit work.
>
> When recycling, we need to count the number of bytes sent, so put xsk
> desc->len into the ptr pointer. Because ptr does not point to meaningful
> objects in xsk.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Reviewed-by: Dust Li <dust.li@linux.alibaba.com>


This needs to be squashed into patch 4.


> ---
>   drivers/net/virtio_net.c | 171 ++++++++++++++++++++++++++-------------
>   1 file changed, 113 insertions(+), 58 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index fac7d0020013..8318b89b2971 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -50,6 +50,9 @@ module_param(xsk_kick_thr, int, 0644);
>   #define VIRTIO_XDP_REDIR	BIT(1)
>   
>   #define VIRTIO_XDP_FLAG	BIT(0)
> +#define VIRTIO_XSK_FLAG	BIT(1)
> +
> +#define VIRTIO_XSK_PTR_SHIFT       4
>   
>   static struct virtio_net_hdr_mrg_rxbuf xsk_hdr;
>   
> @@ -147,6 +150,9 @@ struct send_queue {
>   
>   		/* save the desc for next xmit, when xmit fail. */
>   		struct xdp_desc last_desc;
> +
> +		/* xsk wait for tx inter or softirq */
> +		bool need_wakeup;
>   	} xsk;
>   };
>   
> @@ -266,6 +272,12 @@ struct padded_vnet_hdr {
>   
>   static int virtnet_xsk_run(struct send_queue *sq, struct xsk_buff_pool *pool,
>   			   int budget, bool in_napi);
> +static void virtnet_xsk_complete(struct send_queue *sq, u32 num);
> +
> +static bool is_skb_ptr(void *ptr)
> +{
> +	return !((unsigned long)ptr & (VIRTIO_XDP_FLAG | VIRTIO_XSK_FLAG));
> +}
>   
>   static bool is_xdp_frame(void *ptr)
>   {
> @@ -277,11 +289,58 @@ static void *xdp_to_ptr(struct xdp_frame *ptr)
>   	return (void *)((unsigned long)ptr | VIRTIO_XDP_FLAG);
>   }
>   
> +static void *xsk_to_ptr(struct xdp_desc *desc)
> +{
> +	/* save the desc len to ptr */
> +	u64 p = desc->len << VIRTIO_XSK_PTR_SHIFT;
> +
> +	return (void *)(p | VIRTIO_XSK_FLAG);
> +}
> +
> +static void ptr_to_xsk(void *ptr, struct xdp_desc *desc)
> +{
> +	desc->len = ((u64)ptr) >> VIRTIO_XSK_PTR_SHIFT;
> +}
> +
>   static struct xdp_frame *ptr_to_xdp(void *ptr)
>   {
>   	return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
>   }
>   
> +static void __free_old_xmit(struct send_queue *sq, bool in_napi,
> +			    struct virtnet_sq_stats *stats)
> +{
> +	unsigned int xsknum = 0;
> +	unsigned int len;
> +	void *ptr;
> +
> +	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> +		if (is_skb_ptr(ptr)) {
> +			struct sk_buff *skb = ptr;
> +
> +			pr_debug("Sent skb %p\n", skb);
> +
> +			stats->bytes += skb->len;
> +			napi_consume_skb(skb, in_napi);
> +		} else if (is_xdp_frame(ptr)) {
> +			struct xdp_frame *frame = ptr_to_xdp(ptr);
> +
> +			stats->bytes += frame->len;
> +			xdp_return_frame(frame);
> +		} else {
> +			struct xdp_desc desc;
> +
> +			ptr_to_xsk(ptr, &desc);
> +			stats->bytes += desc.len;
> +			++xsknum;
> +		}
> +		stats->packets++;
> +	}
> +
> +	if (xsknum)
> +		virtnet_xsk_complete(sq, xsknum);
> +}
> +
>   /* Converting between virtqueue no. and kernel tx/rx queue no.
>    * 0:rx0 1:tx0 2:rx1 3:tx1 ... 2N:rxN 2N+1:txN 2N+2:cvq
>    */
> @@ -543,15 +602,12 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>   			    int n, struct xdp_frame **frames, u32 flags)
>   {
>   	struct virtnet_info *vi = netdev_priv(dev);
> +	struct virtnet_sq_stats stats = {};
>   	struct receive_queue *rq = vi->rq;
>   	struct bpf_prog *xdp_prog;
>   	struct send_queue *sq;
> -	unsigned int len;
> -	int packets = 0;
> -	int bytes = 0;
>   	int nxmit = 0;
>   	int kicks = 0;
> -	void *ptr;
>   	int ret;
>   	int i;
>   
> @@ -570,20 +626,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>   	}
>   
>   	/* Free up any pending old buffers before queueing new ones. */
> -	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> -		if (likely(is_xdp_frame(ptr))) {
> -			struct xdp_frame *frame = ptr_to_xdp(ptr);
> -
> -			bytes += frame->len;
> -			xdp_return_frame(frame);
> -		} else {
> -			struct sk_buff *skb = ptr;
> -
> -			bytes += skb->len;
> -			napi_consume_skb(skb, false);
> -		}
> -		packets++;
> -	}
> +	__free_old_xmit(sq, false, &stats);


Let's use a separate patch for this kind of factoring.


>   
>   	for (i = 0; i < n; i++) {
>   		struct xdp_frame *xdpf = frames[i];
> @@ -600,8 +643,8 @@ static int virtnet_xdp_xmit(struct net_device *dev,
>   	}
>   out:
>   	u64_stats_update_begin(&sq->stats.syncp);
> -	sq->stats.bytes += bytes;
> -	sq->stats.packets += packets;
> +	sq->stats.bytes += stats.bytes;
> +	sq->stats.packets += stats.packets;
>   	sq->stats.xdp_tx += n;
>   	sq->stats.xdp_tx_drops += n - nxmit;
>   	sq->stats.kicks += kicks;
> @@ -1426,37 +1469,19 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
>   
>   static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
>   {
> -	unsigned int len;
> -	unsigned int packets = 0;
> -	unsigned int bytes = 0;
> -	void *ptr;
> -
> -	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
> -		if (likely(!is_xdp_frame(ptr))) {
> -			struct sk_buff *skb = ptr;
> +	struct virtnet_sq_stats stats = {};
>   
> -			pr_debug("Sent skb %p\n", skb);
> -
> -			bytes += skb->len;
> -			napi_consume_skb(skb, in_napi);
> -		} else {
> -			struct xdp_frame *frame = ptr_to_xdp(ptr);
> -
> -			bytes += frame->len;
> -			xdp_return_frame(frame);
> -		}
> -		packets++;
> -	}
> +	__free_old_xmit(sq, in_napi, &stats);
>   
>   	/* Avoid overhead when no packets have been processed
>   	 * happens when called speculatively from start_xmit.
>   	 */
> -	if (!packets)
> +	if (!stats.packets)
>   		return;
>   
>   	u64_stats_update_begin(&sq->stats.syncp);
> -	sq->stats.bytes += bytes;
> -	sq->stats.packets += packets;
> +	sq->stats.bytes += stats.bytes;
> +	sq->stats.packets += stats.packets;
>   	u64_stats_update_end(&sq->stats.syncp);
>   }
>   
> @@ -2575,6 +2600,28 @@ static void virtnet_xsk_check_space(struct send_queue *sq)
>   		netif_stop_subqueue(dev, qnum);
>   }
>   
> +static void virtnet_xsk_complete(struct send_queue *sq, u32 num)
> +{
> +	struct xsk_buff_pool *pool;
> +
> +	rcu_read_lock();
> +
> +	pool = rcu_dereference(sq->xsk.pool);
> +	if (!pool) {
> +		rcu_read_unlock();
> +		return;
> +	}
> +
> +	xsk_tx_completed(pool, num);
> +
> +	rcu_read_unlock();
> +
> +	if (sq->xsk.need_wakeup) {
> +		sq->xsk.need_wakeup = false;
> +		virtqueue_napi_schedule(&sq->napi, sq->vq);
> +	}
> +}
> +
>   static int virtnet_xsk_xmit(struct send_queue *sq, struct xsk_buff_pool *pool,
>   			    struct xdp_desc *desc)
>   {
> @@ -2613,7 +2660,8 @@ static int virtnet_xsk_xmit(struct send_queue *sq, struct xsk_buff_pool *pool,
>   			offset = 0;
>   	}
>   
> -	err = virtqueue_add_outbuf(sq->vq, sq->sg, n, NULL, GFP_ATOMIC);
> +	err = virtqueue_add_outbuf(sq->vq, sq->sg, n, xsk_to_ptr(desc),
> +				   GFP_ATOMIC);
>   	if (unlikely(err))
>   		sq->xsk.last_desc = *desc;
>   
> @@ -2623,13 +2671,13 @@ static int virtnet_xsk_xmit(struct send_queue *sq, struct xsk_buff_pool *pool,
>   static int virtnet_xsk_xmit_batch(struct send_queue *sq,
>   				  struct xsk_buff_pool *pool,
>   				  unsigned int budget,
> -				  bool in_napi, int *done)
> +				  bool in_napi, int *done,
> +				  struct virtnet_sq_stats *stats)
>   {
>   	struct xdp_desc desc;
>   	int err, packet = 0;
>   	int ret = -EAGAIN;
>   	int need_kick = 0;
> -	int kicks = 0;
>   
>   	if (sq->xsk.last_desc.addr) {
>   		err = virtnet_xsk_xmit(sq, pool, &sq->xsk.last_desc);
> @@ -2665,7 +2713,7 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
>   		if (need_kick > xsk_kick_thr) {
>   			if (virtqueue_kick_prepare(sq->vq) &&
>   			    virtqueue_notify(sq->vq))
> -				++kicks;
> +				++stats->kicks;
>   
>   			need_kick = 0;
>   		}
> @@ -2675,15 +2723,11 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
>   		if (need_kick) {
>   			if (virtqueue_kick_prepare(sq->vq) &&
>   			    virtqueue_notify(sq->vq))
> -				++kicks;
> -		}
> -		if (kicks) {
> -			u64_stats_update_begin(&sq->stats.syncp);
> -			sq->stats.kicks += kicks;
> -			u64_stats_update_end(&sq->stats.syncp);
> +				++stats->kicks;
>   		}
>   
>   		*done = packet;
> +		stats->xdp_tx += packet;
>   
>   		xsk_tx_release(pool);
>   	}
> @@ -2694,26 +2738,37 @@ static int virtnet_xsk_xmit_batch(struct send_queue *sq,
>   static int virtnet_xsk_run(struct send_queue *sq, struct xsk_buff_pool *pool,
>   			   int budget, bool in_napi)
>   {
> +	struct virtnet_sq_stats stats = {};
>   	int done = 0;
>   	int err;
>   
> -	free_old_xmit_skbs(sq, in_napi);
> +	sq->xsk.need_wakeup = false;
> +	__free_old_xmit(sq, in_napi, &stats);
>   
> -	err = virtnet_xsk_xmit_batch(sq, pool, budget, in_napi, &done);
> +	err = virtnet_xsk_xmit_batch(sq, pool, budget, in_napi, &done, &stats);
>   	/* -EAGAIN: done == budget
>   	 * -EBUSY: done < budget
>   	 *  0    : done < budget
>   	 */
>   	if (err == -EBUSY) {
> -		free_old_xmit_skbs(sq, in_napi);
> +		__free_old_xmit(sq, in_napi, &stats);
>   
>   		/* If the space is enough, let napi run again. */
>   		if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
>   			done = budget;


So I don't see how NAPI can be rescheduled here.

Thanks


> +		else
> +			sq->xsk.need_wakeup = true;
>   	}
>   
>   	virtnet_xsk_check_space(sq);
>   
> +	u64_stats_update_begin(&sq->stats.syncp);
> +	sq->stats.packets += stats.packets;
> +	sq->stats.bytes += stats.bytes;
> +	sq->stats.kicks += stats.kicks;
> +	sq->stats.xdp_tx += stats.xdp_tx;
> +	u64_stats_update_end(&sq->stats.syncp);
> +
>   	return done;
>   }
>   
> @@ -2991,9 +3046,9 @@ static void free_unused_bufs(struct virtnet_info *vi)
>   	for (i = 0; i < vi->max_queue_pairs; i++) {
>   		struct virtqueue *vq = vi->sq[i].vq;
>   		while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) {
> -			if (!is_xdp_frame(buf))
> +			if (is_skb_ptr(buf))
>   				dev_kfree_skb(buf);
> -			else
> +			else if (is_xdp_frame(buf))
>   				xdp_return_frame(ptr_to_xdp(buf));
>   		}
>   	}