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Date:   Tue, 19 Jan 2021 12:44:57 +0000
To:     Xuan Zhuo <xuanzhuo@linux.alibaba.com>
From:   Alexander Lobakin <alobakin@pm.me>
Cc:     Alexander Lobakin <alobakin@pm.me>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, bjorn.topel@intel.com,
        Magnus Karlsson <magnus.karlsson@intel.com>,
        Jonathan Lemon <jonathan.lemon@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        KP Singh <kpsingh@kernel.org>,
        Willem de Bruijn <willemb@google.com>,
        Steffen Klassert <steffen.klassert@secunet.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
        Antoine Tenart <atenart@kernel.org>,
        Michal Kubecek <mkubecek@suse.cz>,
        Andrew Lunn <andrew@lunn.ch>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Meir Lichtinger <meirl@mellanox.com>,
        virtualization@lists.linux-foundation.org, bpf@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Reply-To: Alexander Lobakin <alobakin@pm.me>
Subject: Re: [PATCH bpf-next] xsk: build skb by page
Message-ID: <20210119124406.2895-1-alobakin@pm.me>
In-Reply-To: <579fa463bba42ac71591540a1811dca41d725350.1610764948.git.xuanzhuo@linux.alibaba.com>
References: <579fa463bba42ac71591540a1811dca41d725350.1610764948.git.xuanzhuo@linux.alibaba.com>
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From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Date: Sat, 16 Jan 2021 10:44:53 +0800

> This patch is used to construct skb based on page to save memory copy
> overhead.
>=20
> This has one problem:
>=20
> We construct the skb by fill the data page as a frag into the skb. In
> this way, the linear space is empty, and the header information is also
> in the frag, not in the linear space, which is not allowed for some
> network cards. For example, Mellanox Technologies MT27710 Family
> [ConnectX-4 Lx] will get the following error message:
>=20
>     mlx5_core 0000:3b:00.1 eth1: Error cqe on cqn 0x817, ci 0x8, qn 0x1db=
b, opcode 0xd, syndrome 0x1, vendor syndrome 0x68
>     00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000030: 00 00 00 00 60 10 68 01 0a 00 1d bb 00 0f 9f d2
>     WQE DUMP: WQ size 1024 WQ cur size 0, WQE index 0xf, len: 64
>     00000000: 00 00 0f 0a 00 1d bb 03 00 00 00 08 00 00 00 00
>     00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     00000020: 00 00 00 2b 00 08 00 00 00 00 00 05 9e e3 08 00
>     00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>     mlx5_core 0000:3b:00.1 eth1: ERR CQE on SQ: 0x1dbb
>=20
> I also tried to use build_skb to construct skb, but because of the
> existence of skb_shinfo, it must be behind the linear space, so this
> method is not working. We can't put skb_shinfo on desc->addr, it will be
> exposed to users, this is not safe.
>=20
> Finally, I added a feature NETIF_F_SKB_NO_LINEAR to identify whether the
> network card supports the header information of the packet in the frag
> and not in the linear space.
>=20
> ---------------- Performance Testing ------------
>=20
> The test environment is Aliyun ECS server.
> Test cmd:
> ```
> xdpsock -i eth0 -t  -S -s <msg size>
> ```
>=20
> Test result data:
>=20
> size    64      512     1024    1500
> copy    1916747 1775988 1600203 1440054
> page    1974058 1953655 1945463 1904478
> percent 3.0%    10.0%   21.58%  32.3%
>=20
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
> ---
>  drivers/net/virtio_net.c        |   2 +-
>  include/linux/netdev_features.h |   5 +-
>  net/ethtool/common.c            |   1 +
>  net/xdp/xsk.c                   | 108 +++++++++++++++++++++++++++++++++-=
------
>  4 files changed, 97 insertions(+), 19 deletions(-)
>=20
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 4ecccb8..841a331 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2985,7 +2985,7 @@ static int virtnet_probe(struct virtio_device *vdev=
)
>  =09/* Set up network device as normal. */
>  =09dev->priv_flags |=3D IFF_UNICAST_FLT | IFF_LIVE_ADDR_CHANGE;
>  =09dev->netdev_ops =3D &virtnet_netdev;
> -=09dev->features =3D NETIF_F_HIGHDMA;
> +=09dev->features =3D NETIF_F_HIGHDMA | NETIF_F_SKB_NO_LINEAR;
> =20
>  =09dev->ethtool_ops =3D &virtnet_ethtool_ops;
>  =09SET_NETDEV_DEV(dev, &vdev->dev);
> diff --git a/include/linux/netdev_features.h b/include/linux/netdev_featu=
res.h
> index 934de56..8dd28e2 100644
> --- a/include/linux/netdev_features.h
> +++ b/include/linux/netdev_features.h
> @@ -85,9 +85,11 @@ enum {
> =20
>  =09NETIF_F_HW_MACSEC_BIT,=09=09/* Offload MACsec operations */
> =20
> +=09NETIF_F_SKB_NO_LINEAR_BIT,=09/* Allow skb linear is empty */
> +
>  =09/*
>  =09 * Add your fresh new feature above and remember to update
> -=09 * netdev_features_strings[] in net/core/ethtool.c and maybe
> +=09 * netdev_features_strings[] in net/ethtool/common.c and maybe
>  =09 * some feature mask #defines below. Please also describe it
>  =09 * in Documentation/networking/netdev-features.rst.
>  =09 */
> @@ -157,6 +159,7 @@ enum {
>  #define NETIF_F_GRO_FRAGLIST=09__NETIF_F(GRO_FRAGLIST)
>  #define NETIF_F_GSO_FRAGLIST=09__NETIF_F(GSO_FRAGLIST)
>  #define NETIF_F_HW_MACSEC=09__NETIF_F(HW_MACSEC)
> +#define NETIF_F_SKB_NO_LINEAR=09__NETIF_F(SKB_NO_LINEAR)
> =20
>  /* Finds the next feature with the highest number of the range of start =
till 0.
>   */
> diff --git a/net/ethtool/common.c b/net/ethtool/common.c
> index 24036e3..2f3d309 100644
> --- a/net/ethtool/common.c
> +++ b/net/ethtool/common.c
> @@ -68,6 +68,7 @@
>  =09[NETIF_F_HW_TLS_RX_BIT] =3D=09 "tls-hw-rx-offload",
>  =09[NETIF_F_GRO_FRAGLIST_BIT] =3D=09 "rx-gro-list",
>  =09[NETIF_F_HW_MACSEC_BIT] =3D=09 "macsec-hw-offload",
> +=09[NETIF_F_SKB_NO_LINEAR_BIT] =3D=09 "skb-no-linear",
>  };
> =20
>  const char
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 8037b04..94d17dc 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -430,6 +430,95 @@ static void xsk_destruct_skb(struct sk_buff *skb)
>  =09sock_wfree(skb);
>  }
> =20
> +static struct sk_buff *xsk_build_skb_zerocopy(struct xdp_sock *xs,
> +=09=09=09=09=09      struct xdp_desc *desc)
> +{
> +=09u32 len, offset, copy, copied;
> +=09struct sk_buff *skb;
> +=09struct page *page;
> +=09char *buffer;
> +=09int err, i;
> +=09u64 addr;
> +
> +=09skb =3D sock_alloc_send_skb(&xs->sk, 0, 1, &err);
> +=09if (unlikely(!skb))
> +=09=09return NULL;
> +
> +=09addr =3D desc->addr;
> +=09len =3D desc->len;
> +
> +=09buffer =3D xsk_buff_raw_get_data(xs->pool, addr);
> +=09offset =3D offset_in_page(buffer);
> +=09addr =3D buffer - (char *)xs->pool->addrs;
> +
> +=09for (copied =3D 0, i =3D 0; copied < len; ++i) {

Just noticed. i++ would be less confusing here. You start to fill
skb frags from frag 0 anyway.

> +=09=09page =3D xs->pool->umem->pgs[addr >> PAGE_SHIFT];
> +
> +=09=09get_page(page);
> +
> +=09=09copy =3D min((u32)(PAGE_SIZE - offset), len - copied);

Also. It's better to use min_t() in this case:

copy =3D min_t(u32, PAGE_SIZE - offset, len - copied);

instead of manual casting.

> +=09=09skb_fill_page_desc(skb, i, page, offset, copy);
> +
> +=09=09copied +=3D copy;
> +=09=09addr +=3D copy;
> +=09=09offset =3D 0;
> +=09}
> +
> +=09skb->len +=3D len;
> +=09skb->data_len +=3D len;
> +=09skb->truesize +=3D len;
> +
> +=09refcount_add(len, &xs->sk.sk_wmem_alloc);
> +
> +=09return skb;
> +}
> +
> +static struct sk_buff *xsk_build_skb(struct xdp_sock *xs,
> +=09=09=09=09     struct xdp_desc *desc, int *err)
> +{
> +=09struct sk_buff *skb;
> +
> +=09if (xs->dev->features & NETIF_F_SKB_NO_LINEAR) {
> +=09=09skb =3D xsk_build_skb_zerocopy(xs, desc);
> +=09=09if (unlikely(!skb)) {
> +=09=09=09*err =3D -ENOMEM;
> +=09=09=09return NULL;
> +=09=09}
> +=09} else {
> +=09=09char *buffer;
> +=09=09u64 addr;
> +=09=09u32 len;
> +=09=09int err;
> +
> +=09=09len =3D desc->len;
> +=09=09skb =3D sock_alloc_send_skb(&xs->sk, len, 1, &err);
> +=09=09if (unlikely(!skb)) {
> +=09=09=09*err =3D -ENOMEM;
> +=09=09=09return NULL;
> +=09=09}
> +
> +=09=09skb_put(skb, len);
> +=09=09addr =3D desc->addr;
> +=09=09buffer =3D xsk_buff_raw_get_data(xs->pool, desc->addr);
> +=09=09err =3D skb_store_bits(skb, 0, buffer, len);
> +
> +=09=09if (unlikely(err)) {
> +=09=09=09kfree_skb(skb);
> +=09=09=09*err =3D -EINVAL;
> +=09=09=09return NULL;
> +=09=09}
> +=09}
> +
> +=09skb->dev =3D xs->dev;
> +=09skb->priority =3D xs->sk.sk_priority;
> +=09skb->mark =3D xs->sk.sk_mark;
> +=09skb_shinfo(skb)->destructor_arg =3D (void *)(long)desc->addr;
> +=09skb->destructor =3D xsk_destruct_skb;
> +
> +=09return skb;
> +}
> +
>  static int xsk_generic_xmit(struct sock *sk)
>  {
>  =09struct xdp_sock *xs =3D xdp_sk(sk);
> @@ -446,43 +535,28 @@ static int xsk_generic_xmit(struct sock *sk)
>  =09=09goto out;
> =20
>  =09while (xskq_cons_peek_desc(xs->tx, &desc, xs->pool)) {
> -=09=09char *buffer;
> -=09=09u64 addr;
> -=09=09u32 len;
> -
>  =09=09if (max_batch-- =3D=3D 0) {
>  =09=09=09err =3D -EAGAIN;
>  =09=09=09goto out;
>  =09=09}
> =20
> -=09=09len =3D desc.len;
> -=09=09skb =3D sock_alloc_send_skb(sk, len, 1, &err);
> +=09=09skb =3D xsk_build_skb(xs, &desc, &err);
>  =09=09if (unlikely(!skb))
>  =09=09=09goto out;
> =20
> -=09=09skb_put(skb, len);
> -=09=09addr =3D desc.addr;
> -=09=09buffer =3D xsk_buff_raw_get_data(xs->pool, addr);
> -=09=09err =3D skb_store_bits(skb, 0, buffer, len);
>  =09=09/* This is the backpressure mechanism for the Tx path.
>  =09=09 * Reserve space in the completion queue and only proceed
>  =09=09 * if there is space in it. This avoids having to implement
>  =09=09 * any buffering in the Tx path.
>  =09=09 */
>  =09=09spin_lock_irqsave(&xs->pool->cq_lock, flags);
> -=09=09if (unlikely(err) || xskq_prod_reserve(xs->pool->cq)) {
> +=09=09if (xskq_prod_reserve(xs->pool->cq)) {
>  =09=09=09spin_unlock_irqrestore(&xs->pool->cq_lock, flags);
>  =09=09=09kfree_skb(skb);
>  =09=09=09goto out;
>  =09=09}
>  =09=09spin_unlock_irqrestore(&xs->pool->cq_lock, flags);
> =20
> -=09=09skb->dev =3D xs->dev;
> -=09=09skb->priority =3D sk->sk_priority;
> -=09=09skb->mark =3D sk->sk_mark;
> -=09=09skb_shinfo(skb)->destructor_arg =3D (void *)(long)desc.addr;
> -=09=09skb->destructor =3D xsk_destruct_skb;
> -
>  =09=09err =3D __dev_direct_xmit(skb, xs->queue_id);
>  =09=09if  (err =3D=3D NETDEV_TX_BUSY) {
>  =09=09=09/* Tell user-space to retry the send */
> --=20
> 1.8.3.1

Al