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Date: Thu, 3 Feb 2022 15:04:48 +0200
From: Tariq Toukan <ttoukan.linux@...il.com>
To: Eric Dumazet <eric.dumazet@...il.com>,
"David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>
Cc: netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
Coco Li <lixiaoyan@...gle.com>,
Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH net-next 14/15] mlx4: support BIG TCP packets
On 2/3/2022 3:51 AM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> mlx4 supports LSOv2 just fine.
>
> IPv6 stack inserts a temporary Hop-by-Hop header
> with JUMBO TLV for big packets.
>
> We need to ignore the HBH header when populating TX descriptor.
>
> Tested:
>
> Before: (not enabling bigger TSO/GRO packets)
>
> ip link set dev eth0 gso_ipv6_max_size 65536 gro_ipv6_max_size 65536
>
> netperf -H lpaa18 -t TCP_RR -T2,2 -l 10 -Cc -- -r 70000,70000
> MIGRATED TCP REQUEST/RESPONSE TEST from ::0 (::) port 0 AF_INET6 to lpaa18.prod.google.com () port 0 AF_INET6 : first burst 0 : cpu bind
> Local /Remote
> Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem
> Send Recv Size Size Time Rate local remote local remote
> bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr
>
> 262144 540000 70000 70000 10.00 6591.45 0.86 1.34 62.490 97.446
> 262144 540000
>
> After: (enabling bigger TSO/GRO packets)
>
> ip link set dev eth0 gso_ipv6_max_size 185000 gro_ipv6_max_size 185000
>
> netperf -H lpaa18 -t TCP_RR -T2,2 -l 10 -Cc -- -r 70000,70000
> MIGRATED TCP REQUEST/RESPONSE TEST from ::0 (::) port 0 AF_INET6 to lpaa18.prod.google.com () port 0 AF_INET6 : first burst 0 : cpu bind
> Local /Remote
> Socket Size Request Resp. Elapsed Trans. CPU CPU S.dem S.dem
> Send Recv Size Size Time Rate local remote local remote
> bytes bytes bytes bytes secs. per sec % S % S us/Tr us/Tr
>
> 262144 540000 70000 70000 10.00 8383.95 0.95 1.01 54.432 57.584
> 262144 540000
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Tariq Toukan <tariqt@...dia.com>
> ---
> .../net/ethernet/mellanox/mlx4/en_netdev.c | 3 ++
> drivers/net/ethernet/mellanox/mlx4/en_tx.c | 47 +++++++++++++++----
> 2 files changed, 41 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> index c61dc7ae0c056a4dbcf24297549f6b1b5cc25d92..76cb93f5e5240c54f6f4c57e39739376206b4f34 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> @@ -3417,6 +3417,9 @@ int mlx4_en_init_netdev(struct mlx4_en_dev *mdev, int port,
> dev->min_mtu = ETH_MIN_MTU;
> dev->max_mtu = priv->max_mtu;
>
> + /* supports LSOv2 packets, 512KB limit has been tested. */
> + netif_set_tso_ipv6_max_size(dev, 512 * 1024);
> +
> mdev->pndev[port] = dev;
> mdev->upper[port] = NULL;
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
> index 817f4154b86d599cd593876ec83529051d95fe2f..c89b3e8094e7d8cfb11aaa6cc4ad63bf3ad5934e 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
> @@ -44,6 +44,7 @@
> #include <linux/ipv6.h>
> #include <linux/moduleparam.h>
> #include <linux/indirect_call_wrapper.h>
> +#include <net/ipv6.h>
>
> #include "mlx4_en.h"
>
> @@ -635,19 +636,28 @@ static int get_real_size(const struct sk_buff *skb,
> struct net_device *dev,
> int *lso_header_size,
> bool *inline_ok,
> - void **pfrag)
> + void **pfrag,
> + int *hopbyhop)
> {
> struct mlx4_en_priv *priv = netdev_priv(dev);
> int real_size;
>
> if (shinfo->gso_size) {
> *inline_ok = false;
> - if (skb->encapsulation)
> + *hopbyhop = 0;
> + if (skb->encapsulation) {
> *lso_header_size = (skb_inner_transport_header(skb) - skb->data) + inner_tcp_hdrlen(skb);
> - else
> + } else {
> + /* Detects large IPV6 TCP packets and prepares for removal of
> + * HBH header that has been pushed by ip6_xmit(),
> + * mainly so that tcpdump can dissect them.
> + */
> + if (ipv6_has_hopopt_jumbo(skb))
> + *hopbyhop = sizeof(struct hop_jumbo_hdr);
> *lso_header_size = skb_transport_offset(skb) + tcp_hdrlen(skb);
> + }
> real_size = CTRL_SIZE + shinfo->nr_frags * DS_SIZE +
> - ALIGN(*lso_header_size + 4, DS_SIZE);
> + ALIGN(*lso_header_size - *hopbyhop + 4, DS_SIZE);
> if (unlikely(*lso_header_size != skb_headlen(skb))) {
> /* We add a segment for the skb linear buffer only if
> * it contains data */
> @@ -874,6 +884,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
> int desc_size;
> int real_size;
> u32 index, bf_index;
> + struct ipv6hdr *h6;
> __be32 op_own;
> int lso_header_size;
> void *fragptr = NULL;
> @@ -882,6 +893,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
> bool stop_queue;
> bool inline_ok;
> u8 data_offset;
> + int hopbyhop;
> bool bf_ok;
>
> tx_ind = skb_get_queue_mapping(skb);
> @@ -891,7 +903,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
> goto tx_drop;
>
> real_size = get_real_size(skb, shinfo, dev, &lso_header_size,
> - &inline_ok, &fragptr);
> + &inline_ok, &fragptr, &hopbyhop);
> if (unlikely(!real_size))
> goto tx_drop_count;
>
> @@ -944,7 +956,7 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
> data = &tx_desc->data;
> data_offset = offsetof(struct mlx4_en_tx_desc, data);
> } else {
> - int lso_align = ALIGN(lso_header_size + 4, DS_SIZE);
> + int lso_align = ALIGN(lso_header_size - hopbyhop + 4, DS_SIZE);
>
> data = (void *)&tx_desc->lso + lso_align;
> data_offset = offsetof(struct mlx4_en_tx_desc, lso) + lso_align;
> @@ -1009,14 +1021,31 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
> ((ring->prod & ring->size) ?
> cpu_to_be32(MLX4_EN_BIT_DESC_OWN) : 0);
>
> + lso_header_size -= hopbyhop;
> /* Fill in the LSO prefix */
> tx_desc->lso.mss_hdr_size = cpu_to_be32(
> shinfo->gso_size << 16 | lso_header_size);
>
> - /* Copy headers;
> - * note that we already verified that it is linear */
> - memcpy(tx_desc->lso.header, skb->data, lso_header_size);
>
> + if (unlikely(hopbyhop)) {
> + /* remove the HBH header.
> + * Layout: [Ethernet header][IPv6 header][HBH][TCP header]
> + */
> + memcpy(tx_desc->lso.header, skb->data, ETH_HLEN + sizeof(*h6));
> + h6 = (struct ipv6hdr *)((char *)tx_desc->lso.header + ETH_HLEN);
> + h6->nexthdr = IPPROTO_TCP;
> + /* Copy the TCP header after the IPv6 one */
> + memcpy(h6 + 1,
> + skb->data + ETH_HLEN + sizeof(*h6) +
> + sizeof(struct hop_jumbo_hdr),
> + tcp_hdrlen(skb));
> + /* Leave ipv6 payload_len set to 0, as LSO v2 specs request. */
Hi Eric,
Many thanks for your patches.
Impressive improvement indeed!
I am concerned about not using lso_header_size in this flow.
The num of bytes copied here might be out-of-sync with the value
provided in the descriptor (tx_desc->lso.mss_hdr_size).
Are the two values guaranteed to be equal?
I think this is an assumption that can get broken in the future by
unaware patches to the kernel stack.
Thanks,
Tariq
> + } else {
> + /* Copy headers;
> + * note that we already verified that it is linear
> + */
> + memcpy(tx_desc->lso.header, skb->data, lso_header_size);
> + }
> ring->tso_packets++;
>
> i = shinfo->gso_segs;
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