From: Xuan Zhuo <xuanz...@linux.alibaba.com>
Date: Tue, 19 Jan 2021 17:45:12 +0800
> 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 <xuanz...@linux.alibaba.com>
> Reviewed-by: Dust Li <dust...@linux.alibaba.com>
> ---
> net/xdp/xsk.c | 112
> ++++++++++++++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 94 insertions(+), 18 deletions(-)
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 8037b04..8c291f8 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -430,6 +430,95 @@ 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)
> +{
> + u32 len, offset, copy, copied;
> + struct sk_buff *skb;
> + struct page *page;
> + char *buffer;
> + int err = 0, i;
> + u64 addr;
> +
> + skb = sock_alloc_send_skb(&xs->sk, 0, 1, &err);
> + if (unlikely(!skb))
> + return NULL;
You can propagate err from here to the outer function:
if (unlikely(!skb))
return ERR_PTR(err);
> + addr = desc->addr;
> + len = desc->len;
> +
> + buffer = xsk_buff_raw_get_data(xs->pool, addr);
> + offset = offset_in_page(buffer);
> + addr = buffer - (char *)xs->pool->addrs;
> +
> + for (copied = 0, i = 0; copied < len; ++i) {
i++ would be less confusing here. You build skb frags from frag 0
anyway.
> + page = xs->pool->umem->pgs[addr >> PAGE_SHIFT];
> +
> + get_page(page);
> +
> + copy = min((u32)(PAGE_SIZE - offset), len - copied);
It's better to use min_t(u32, ...) instead of manual casting.
> +
> + skb_fill_page_desc(skb, i, page, offset, copy);
> +
> + copied += copy;
> + addr += copy;
> + offset = 0;
> + }
> +
> + skb->len += len;
> + skb->data_len += len;
> + skb->truesize += len;
> +
> + refcount_add(len, &xs->sk.sk_wmem_alloc);
> +
> + return skb;
> +}
> +
> +static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
> + struct xdp_desc *desc)
> +{
> + struct sk_buff *skb = NULL;
> + int err = -ENOMEM;
> +
> + if (xs->dev->priv_flags & IFF_TX_SKB_NO_LINEAR) {
> + skb = xsk_build_skb_zerocopy(xs, desc);
> + if (unlikely(!skb))
> + goto err;
1. You should'n use goto err here, as skb == NULL, so kfree_skb(skb)
is redundant.
2. If you would use ERR_PTR() in xsk_build_skb_zerocopy(),
the condition should look like:
if (IS_ERR(skb))
return PTR_ERR(skb);
> + } else {
> + char *buffer;
> + u64 addr;
> + u32 len;
> + int err;
> +
> + len = desc->len;
> + skb = sock_alloc_send_skb(&xs->sk, len, 1, &err);
> + if (unlikely(!skb))
> + goto err;
Same here, if skb == NULL, just return without calling kfree_skb().
> + skb_put(skb, len);
> + addr = desc->addr;
> + buffer = xsk_buff_raw_get_data(xs->pool, desc->addr);
> + err = skb_store_bits(skb, 0, buffer, len);
> +
> + if (unlikely(err)) {
> + err = -EINVAL;
You already have errno in err, no need to override it.
> + goto err;
> + }
> + }
> +
> + skb->dev = xs->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;
> +
> +err:
> + kfree_skb(skb);
> + return ERR_PTR(err);
> +}
> +
> static int xsk_generic_xmit(struct sock *sk)
> {
> struct xdp_sock *xs = xdp_sk(sk);
> @@ -446,43 +535,30 @@ static int xsk_generic_xmit(struct sock *sk)
> goto out;
>
> 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, len, 1, &err);
> - if (unlikely(!skb))
> + skb = xsk_build_skb(xs, &desc);
> + if (IS_ERR(skb)) {
> + err = PTR_ERR(skb);
> goto out;
> + }
>
> - 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 */
So please recheck the code and then retest it, especially error
paths (you can inject errors manually here to ensure they work).
Thanks,
Al
