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: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210218204908.5455-6-alobakin@pm.me

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 143979e..a71ed66 100644 (file)
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -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 */