Commit 9c8f21e6 authored by Xuan Zhuo's avatar Xuan Zhuo Committed by Daniel Borkmann
Browse files

xsk: Build skb by page (aka generic zerocopy xmit) 



This patch is used to construct skb based on page to save memory copy
overhead.

This function is implemented based on IFF_TX_SKB_NO_LINEAR. Only the
network card priv_flags supports IFF_TX_SKB_NO_LINEAR will use page to
directly construct skb. If this feature is not supported, it is still
necessary to copy data to construct skb.

  ---------------- Performance Testing ------------

  The test environment is Aliyun ECS server.

  Test cmd:
  ```
  xdpsock -i eth0 -t  -S -s <msg size>
  ```

  Test result data:

  size    64      512     1024    1500
  copy    1916747 1775988 1600203 1440054
  page    1974058 1953655 1945463 1904478
  percent 3.0%    10.0%   21.58%  32.3%

Signed-off-by: default avatarXuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: default avatarAlexander Lobakin <alobakin@pm.me>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarDust Li <dust.li@linux.alibaba.com>
Acked-by: default avatarMagnus Karlsson <magnus.karlsson@intel.com>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210218204908.5455-6-alobakin@pm.me
parent 3914d88f

net/xdp/xsk.c

+96 −24
Original line number Diff line number Diff line
@@ -445,6 +445,97 @@ static void xsk_destruct_skb(struct sk_buff *skb) 
	sock_wfree(skb);

}



static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,

					      struct xdp_desc *desc)

{

	struct xsk_buff_pool *pool = xs->pool;

	u32 hr, len, ts, offset, copy, copied;

	struct sk_buff *skb;

	struct page *page;

	void *buffer;

	int err, i;

	u64 addr;



	hr = max(NET_SKB_PAD, L1_CACHE_ALIGN(xs->dev->needed_headroom));



	skb = sock_alloc_send_skb(&xs->sk, hr, 1, &err);

	if (unlikely(!skb))

		return ERR_PTR(err);



	skb_reserve(skb, hr);



	addr = desc->addr;

	len = desc->len;

	ts = pool->unaligned ? len : pool->chunk_size;



	buffer = xsk_buff_raw_get_data(pool, addr);

	offset = offset_in_page(buffer);

	addr = buffer - pool->addrs;



	for (copied = 0, i = 0; copied < len; i++) {

		page = pool->umem->pgs[addr >> PAGE_SHIFT];

		get_page(page);



		copy = min_t(u32, PAGE_SIZE - offset, len - copied);

		skb_fill_page_desc(skb, i, page, offset, copy);



		copied += copy;

		addr += copy;

		offset = 0;

	}



	skb->len += len;

	skb->data_len += len;

	skb->truesize += ts;



	refcount_add(ts, &xs->sk.sk_wmem_alloc);



	return skb;

}



static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,

				     struct xdp_desc *desc)

{

	struct net_device *dev = xs->dev;

	struct sk_buff *skb;



	if (dev->priv_flags & IFF_TX_SKB_NO_LINEAR) {

		skb = xsk_build_skb_zerocopy(xs, desc);

		if (IS_ERR(skb))

			return skb;

	} else {

		u32 hr, tr, len;

		void *buffer;

		int err;



		hr = max(NET_SKB_PAD, L1_CACHE_ALIGN(dev->needed_headroom));

		tr = dev->needed_tailroom;

		len = desc->len;



		skb = sock_alloc_send_skb(&xs->sk, hr + len + tr, 1, &err);

		if (unlikely(!skb))

			return ERR_PTR(err);



		skb_reserve(skb, hr);

		skb_put(skb, len);



		buffer = xsk_buff_raw_get_data(xs->pool, desc->addr);

		err = skb_store_bits(skb, 0, buffer, len);

		if (unlikely(err)) {

			kfree_skb(skb);

			return ERR_PTR(err);

		}

	}



	skb->dev = dev;

	skb->priority = xs->sk.sk_priority;

	skb->mark = xs->sk.sk_mark;

	skb_shinfo(skb)->destructor_arg = (void *)(long)desc->addr;

	skb->destructor = xsk_destruct_skb;



	return skb;

}



static int xsk_generic_xmit(struct sock *sk)

{

	struct xdp_sock *xs = xdp_sk(sk);
@@ -454,56 +545,37 @@ static int xsk_generic_xmit(struct sock *sk) 
	struct sk_buff *skb;

	unsigned long flags;

	int err = 0;

	u32 hr, tr;



	mutex_lock(&xs->mutex);



	if (xs->queue_id >= xs->dev->real_num_tx_queues)

		goto out;



	hr = max(NET_SKB_PAD, L1_CACHE_ALIGN(xs->dev->needed_headroom));

	tr = xs->dev->needed_tailroom;



	while (xskq_cons_peek_desc(xs->tx, &desc, xs->pool)) {

		char *buffer;

		u64 addr;

		u32 len;



		if (max_batch-- == 0) {

			err = -EAGAIN;

			goto out;

		}



		len = desc.len;

		skb = sock_alloc_send_skb(sk, hr + len + tr, 1, &err);

		if (unlikely(!skb))

		skb = xsk_build_skb(xs, &desc);

		if (IS_ERR(skb)) {

			err = PTR_ERR(skb);

			goto out;

		}



		skb_reserve(skb, hr);

		skb_put(skb, len);



		addr = desc.addr;

		buffer = xsk_buff_raw_get_data(xs->pool, addr);

		err = skb_store_bits(skb, 0, buffer, len);

		/* This is the backpressure mechanism for the Tx path.

		 * Reserve space in the completion queue and only proceed

		 * if there is space in it. This avoids having to implement

		 * any buffering in the Tx path.

		 */

		spin_lock_irqsave(&xs->pool->cq_lock, flags);

		if (unlikely(err) || xskq_prod_reserve(xs->pool->cq)) {

		if (xskq_prod_reserve(xs->pool->cq)) {

			spin_unlock_irqrestore(&xs->pool->cq_lock, flags);

			kfree_skb(skb);

			goto out;

		}

		spin_unlock_irqrestore(&xs->pool->cq_lock, flags);



		skb->dev = xs->dev;

		skb->priority = sk->sk_priority;

		skb->mark = sk->sk_mark;

		skb_shinfo(skb)->destructor_arg = (void *)(long)desc.addr;

		skb->destructor = xsk_destruct_skb;



		err = __dev_direct_xmit(skb, xs->queue_id);

		if  (err == NETDEV_TX_BUSY) {

			/* Tell user-space to retry the send */