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Message-ID: <8e4cd169-f1b7-0f39-eaad-8cf441077f84@gmail.com>
Date: Sun, 31 Jan 2021 12:40:09 +0200
From: Boris Pismenny <borispismenny@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Boris Pismenny <borisp@...lanox.com>,
Jakub Kicinski <kuba@...nel.org>,
David Miller <davem@...emloft.net>,
Saeed Mahameed <saeedm@...dia.com>,
Christoph Hellwig <hch@....de>, sagi@...mberg.me, axboe@...com,
kbusch@...nel.org, Al Viro <viro@...iv.linux.org.uk>,
David Ahern <dsahern@...il.com>, smalin@...vell.com,
boris.pismenny@...il.com, linux-nvme@...ts.infradead.org,
netdev <netdev@...r.kernel.org>, benishay@...dia.com,
ogerlitz@...dia.com, yorayz@...dia.com,
Ben Ben-Ishay <benishay@...lanox.com>,
Or Gerlitz <ogerlitz@...lanox.com>,
Yoray Zack <yorayz@...lanox.com>
Subject: Re: [PATCH v2 net-next 02/21] net: Introduce direct data placement
tcp offload
On 14/01/2021 22:43, Eric Dumazet wrote:
> On Thu, Jan 14, 2021 at 9:19 PM Boris Pismenny <borispismenny@...il.com> wrote:
>>
>>
>>
>> On 14/01/2021 17:57, Eric Dumazet wrote:
>>> On Thu, Jan 14, 2021 at 4:10 PM Boris Pismenny <borisp@...lanox.com> wrote:
>>>>
>>>> This commit introduces direct data placement offload for TCP.
>>>> This capability is accompanied by new net_device operations that
>>>> configure hardware contexts. There is a context per socket, and a context per DDP
>>>> opreation. Additionally, a resynchronization routine is used to assist
>>>> hardware handle TCP OOO, and continue the offload.
>>>> Furthermore, we let the offloading driver advertise what is the max hw
>>>> sectors/segments.
>>>>
>>>> Using this interface, the NIC hardware will scatter TCP payload directly
>>>> to the BIO pages according to the command_id.
>>>> To maintain the correctness of the network stack, the driver is expected
>>>> to construct SKBs that point to the BIO pages.
>>>>
>>>> This, the SKB represents the data on the wire, while it is pointing
>>>> to data that is already placed in the destination buffer.
>>>> As a result, data from page frags should not be copied out to
>>>> the linear part.
>>>>
>>>> As SKBs that use DDP are already very memory efficient, we modify
>>>> skb_condence to avoid copying data from fragments to the linear
>>>> part of SKBs that belong to a socket that uses DDP offload.
>>>>
>>>> A follow-up patch will use this interface for DDP in NVMe-TCP.
>>>>
>>>> Signed-off-by: Boris Pismenny <borisp@...lanox.com>
>>>> Signed-off-by: Ben Ben-Ishay <benishay@...lanox.com>
>>>> Signed-off-by: Or Gerlitz <ogerlitz@...lanox.com>
>>>> Signed-off-by: Yoray Zack <yorayz@...lanox.com>
>>>> ---
>>>> include/linux/netdev_features.h | 2 +
>>>> include/linux/netdevice.h | 5 ++
>>>> include/net/inet_connection_sock.h | 4 +
>>>> include/net/tcp_ddp.h | 136 +++++++++++++++++++++++++++++
>>>> net/Kconfig | 9 ++
>>>> net/core/skbuff.c | 9 +-
>>>> net/ethtool/common.c | 1 +
>>>> 7 files changed, 165 insertions(+), 1 deletion(-)
>>>> create mode 100644 include/net/tcp_ddp.h
>>>>
>>>> diff --git a/include/linux/netdev_features.h b/include/linux/netdev_features.h
>>>> index 934de56644e7..fb35dcac03d2 100644
>>>> --- a/include/linux/netdev_features.h
>>>> +++ b/include/linux/netdev_features.h
>>>> @@ -84,6 +84,7 @@ enum {
>>>> NETIF_F_GRO_FRAGLIST_BIT, /* Fraglist GRO */
>>>>
>>>> NETIF_F_HW_MACSEC_BIT, /* Offload MACsec operations */
>>>> + NETIF_F_HW_TCP_DDP_BIT, /* TCP direct data placement offload */
>>>>
>>>> /*
>>>> * Add your fresh new feature above and remember to update
>>>> @@ -157,6 +158,7 @@ enum {
>>>> #define NETIF_F_GRO_FRAGLIST __NETIF_F(GRO_FRAGLIST)
>>>> #define NETIF_F_GSO_FRAGLIST __NETIF_F(GSO_FRAGLIST)
>>>> #define NETIF_F_HW_MACSEC __NETIF_F(HW_MACSEC)
>>>> +#define NETIF_F_HW_TCP_DDP __NETIF_F(HW_TCP_DDP)
>>>>
>>>> /* Finds the next feature with the highest number of the range of start till 0.
>>>> */
>>>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>>>> index 259be67644e3..3dd3cdf5dec3 100644
>>>> --- a/include/linux/netdevice.h
>>>> +++ b/include/linux/netdevice.h
>>>> @@ -941,6 +941,7 @@ struct dev_ifalias {
>>>>
>>>> struct devlink;
>>>> struct tlsdev_ops;
>>>> +struct tcp_ddp_dev_ops;
>>>>
>>>> struct netdev_name_node {
>>>> struct hlist_node hlist;
>>>> @@ -1937,6 +1938,10 @@ struct net_device {
>>>> const struct tlsdev_ops *tlsdev_ops;
>>>> #endif
>>>>
>>>> +#ifdef CONFIG_TCP_DDP
>>>> + const struct tcp_ddp_dev_ops *tcp_ddp_ops;
>>>> +#endif
>>>> +
>>>> const struct header_ops *header_ops;
>>>>
>>>> unsigned int flags;
>>>> diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
>>>> index 7338b3865a2a..a08b85b53aa8 100644
>>>> --- a/include/net/inet_connection_sock.h
>>>> +++ b/include/net/inet_connection_sock.h
>>>> @@ -66,6 +66,8 @@ struct inet_connection_sock_af_ops {
>>>> * @icsk_ulp_ops Pluggable ULP control hook
>>>> * @icsk_ulp_data ULP private data
>>>> * @icsk_clean_acked Clean acked data hook
>>>> + * @icsk_ulp_ddp_ops Pluggable ULP direct data placement control hook
>>>> + * @icsk_ulp_ddp_data ULP direct data placement private data
>>>> * @icsk_listen_portaddr_node hash to the portaddr listener hashtable
>>>> * @icsk_ca_state: Congestion control state
>>>> * @icsk_retransmits: Number of unrecovered [RTO] timeouts
>>>> @@ -94,6 +96,8 @@ struct inet_connection_sock {
>>>> const struct tcp_ulp_ops *icsk_ulp_ops;
>>>> void __rcu *icsk_ulp_data;
>>>> void (*icsk_clean_acked)(struct sock *sk, u32 acked_seq);
>>>
>>> #ifdef CONFIG_TCP_DDP ?
>>>
>>>> + const struct tcp_ddp_ulp_ops *icsk_ulp_ddp_ops;
>>>> + void __rcu *icsk_ulp_ddp_data;
>>>> struct hlist_node icsk_listen_portaddr_node;
>>>> unsigned int (*icsk_sync_mss)(struct sock *sk, u32 pmtu);
>>>> __u8 icsk_ca_state:5,
>>>> diff --git a/include/net/tcp_ddp.h b/include/net/tcp_ddp.h
>>>> new file mode 100644
>>>> index 000000000000..31e5b1a16d0f
>>>> --- /dev/null
>>>> +++ b/include/net/tcp_ddp.h
>>>> @@ -0,0 +1,136 @@
>>>> +/* SPDX-License-Identifier: GPL-2.0
>>>> + *
>>>> + * tcp_ddp.h
>>>> + * Author: Boris Pismenny <borisp@...lanox.com>
>>>> + * Copyright (C) 2021 Mellanox Technologies.
>>>> + */
>>>> +#ifndef _TCP_DDP_H
>>>> +#define _TCP_DDP_H
>>>> +
>>>> +#include <linux/netdevice.h>
>>>> +#include <net/inet_connection_sock.h>
>>>> +#include <net/sock.h>
>>>> +
>>>> +/* limits returned by the offload driver, zero means don't care */
>>>> +struct tcp_ddp_limits {
>>>> + int max_ddp_sgl_len;
>>>> +};
>>>> +
>>>> +enum tcp_ddp_type {
>>>> + TCP_DDP_NVME = 1,
>>>> +};
>>>> +
>>>> +/**
>>>> + * struct tcp_ddp_config - Generic tcp ddp configuration: tcp ddp IO queue
>>>> + * config implementations must use this as the first member.
>>>> + * Add new instances of tcp_ddp_config below (nvme-tcp, etc.).
>>>> + */
>>>> +struct tcp_ddp_config {
>>>> + enum tcp_ddp_type type;
>>>> + unsigned char buf[];
>>>> +};
>>>> +
>>>> +/**
>>>> + * struct nvme_tcp_ddp_config - nvme tcp ddp configuration for an IO queue
>>>> + *
>>>> + * @pfv: pdu version (e.g., NVME_TCP_PFV_1_0)
>>>> + * @cpda: controller pdu data alignmend (dwords, 0's based)
>>>> + * @dgst: digest types enabled.
>>>> + * The netdev will offload crc if ddp_crc is supported.
>>>> + * @queue_size: number of nvme-tcp IO queue elements
>>>> + * @queue_id: queue identifier
>>>> + * @cpu_io: cpu core running the IO thread for this queue
>>>> + */
>>>> +struct nvme_tcp_ddp_config {
>>>> + struct tcp_ddp_config cfg;
>>>> +
>>>> + u16 pfv;
>>>> + u8 cpda;
>>>> + u8 dgst;
>>>> + int queue_size;
>>>> + int queue_id;
>>>> + int io_cpu;
>>>> +};
>>>> +
>>>> +/**
>>>> + * struct tcp_ddp_io - tcp ddp configuration for an IO request.
>>>> + *
>>>> + * @command_id: identifier on the wire associated with these buffers
>>>> + * @nents: number of entries in the sg_table
>>>> + * @sg_table: describing the buffers for this IO request
>>>> + * @first_sgl: first SGL in sg_table
>>>> + */
>>>> +struct tcp_ddp_io {
>>>> + u32 command_id;
>>>> + int nents;
>>>> + struct sg_table sg_table;
>>>> + struct scatterlist first_sgl[SG_CHUNK_SIZE];
>>>> +};
>>>> +
>>>> +/* struct tcp_ddp_dev_ops - operations used by an upper layer protocol to configure ddp offload
>>>> + *
>>>> + * @tcp_ddp_limits: limit the number of scatter gather entries per IO.
>>>> + * the device driver can use this to limit the resources allocated per queue.
>>>> + * @tcp_ddp_sk_add: add offload for the queue represennted by the socket+config pair.
>>>> + * this function is used to configure either copy, crc or both offloads.
>>>> + * @tcp_ddp_sk_del: remove offload from the socket, and release any device related resources.
>>>> + * @tcp_ddp_setup: request copy offload for buffers associated with a command_id in tcp_ddp_io.
>>>> + * @tcp_ddp_teardown: release offload resources association between buffers and command_id in
>>>> + * tcp_ddp_io.
>>>> + * @tcp_ddp_resync: respond to the driver's resync_request. Called only if resync is successful.
>>>> + */
>>>> +struct tcp_ddp_dev_ops {
>>>> + int (*tcp_ddp_limits)(struct net_device *netdev,
>>>> + struct tcp_ddp_limits *limits);
>>>> + int (*tcp_ddp_sk_add)(struct net_device *netdev,
>>>> + struct sock *sk,
>>>> + struct tcp_ddp_config *config);
>>>> + void (*tcp_ddp_sk_del)(struct net_device *netdev,
>>>> + struct sock *sk);
>>>> + int (*tcp_ddp_setup)(struct net_device *netdev,
>>>> + struct sock *sk,
>>>> + struct tcp_ddp_io *io);
>>>> + int (*tcp_ddp_teardown)(struct net_device *netdev,
>>>> + struct sock *sk,
>>>> + struct tcp_ddp_io *io,
>>>> + void *ddp_ctx);
>>>> + void (*tcp_ddp_resync)(struct net_device *netdev,
>>>> + struct sock *sk, u32 seq);
>>>> +};
>>>> +
>>>> +#define TCP_DDP_RESYNC_REQ BIT(0)
>>>> +
>>>> +/**
>>>> + * struct tcp_ddp_ulp_ops - Interface to register uppper layer Direct Data Placement (DDP) TCP offload
>>>> + */
>>>> +struct tcp_ddp_ulp_ops {
>>>> + /* NIC requests ulp to indicate if @seq is the start of a message */
>>>> + bool (*resync_request)(struct sock *sk, u32 seq, u32 flags);
>>>> + /* NIC driver informs the ulp that ddp teardown is done - used for async completions*/
>>>> + void (*ddp_teardown_done)(void *ddp_ctx);
>>>> +};
>>>> +
>>>> +/**
>>>> + * struct tcp_ddp_ctx - Generic tcp ddp context: device driver per queue contexts must
>>>> + * use this as the first member.
>>>> + */
>>>> +struct tcp_ddp_ctx {
>>>> + enum tcp_ddp_type type;
>>>> + unsigned char buf[];
>>>> +};
>>>> +
>>>> +static inline struct tcp_ddp_ctx *tcp_ddp_get_ctx(const struct sock *sk)
>>>> +{
>>>> + struct inet_connection_sock *icsk = inet_csk(sk);
>>>> +
>>>> + return (__force struct tcp_ddp_ctx *)icsk->icsk_ulp_ddp_data;
>>>> +}
>>>> +
>>>> +static inline void tcp_ddp_set_ctx(struct sock *sk, void *ctx)
>>>> +{
>>>> + struct inet_connection_sock *icsk = inet_csk(sk);
>>>> +
>>>> + rcu_assign_pointer(icsk->icsk_ulp_ddp_data, ctx);
>>>> +}
>>>> +
>>>> +#endif //_TCP_DDP_H
>>>> diff --git a/net/Kconfig b/net/Kconfig
>>>> index f4c32d982af6..3876861cdc90 100644
>>>> --- a/net/Kconfig
>>>> +++ b/net/Kconfig
>>>> @@ -457,6 +457,15 @@ config ETHTOOL_NETLINK
>>>> netlink. It provides better extensibility and some new features,
>>>> e.g. notification messages.
>>>>
>>>> +config TCP_DDP
>>>> + bool "TCP direct data placement offload"
>>>> + default n
>>>> + help
>>>> + Direct Data Placement (DDP) offload for TCP enables ULP, such as
>>>> + NVMe-TCP/iSCSI, to request the NIC to place TCP payload data
>>>> + of a command response directly into kernel pages.
>>>> +
>>>> +
>>>> endif # if NET
>>>>
>>>> # Used by archs to tell that they support BPF JIT compiler plus which flavour.
>>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>>>> index f62cae3f75d8..791c1b6bc067 100644
>>>> --- a/net/core/skbuff.c
>>>> +++ b/net/core/skbuff.c
>>>> @@ -69,6 +69,7 @@
>>>> #include <net/xfrm.h>
>>>> #include <net/mpls.h>
>>>> #include <net/mptcp.h>
>>>> +#include <net/tcp_ddp.h>
>>>>
>>>> #include <linux/uaccess.h>
>>>> #include <trace/events/skb.h>
>>>> @@ -6140,9 +6141,15 @@ EXPORT_SYMBOL(pskb_extract);
>>>> */
>>>> void skb_condense(struct sk_buff *skb)
>>>> {
>>>> + bool is_ddp = false;
>>>> +
>>>> +#ifdef CONFIG_TCP_DDP
>>>
>>> This looks strange to me : TCP should call this helper while skb->sk is NULL
>>>
>>> Are you sure this is not dead code ?
>>>
>>
>> Will verify again on Sunday. AFAICT, early demux sets skb->sk before this code
>> is called.
>
>
> First, early demux is optional.
>
> Secondly, skb->sk is stolen in skb_steal_sock() if early demux was performed.
>
>
> Just to clarify, the purpose of this code is to avoid skb condensing
>> data that is already placed into destination buffers.
>
> Then this has not been tested. This suggests this code could be
> removed, I doubt that your target traffic would ever be 'condensed'.
>
Thanks for the feedback!
Some retrospective about this:
We originally used the skb->ddp_crc bit for this check, but later we
tried to avoid it so as to reduce our dependence on said skb bit.
Unfortunately, that later change wasn't tested thoroughly.
We'll post v3 patches that will use the skb->ddp_crc bit for this check.
After re-testing with the new v3 patch I'm confident it will work.
>>
>>>> + is_ddp = skb->sk && inet_csk(skb->sk) &&
>>>> + inet_csk(skb->sk)->icsk_ulp_ddp_data;
>>>> +#endif
>>>> if (skb->data_len) {
>>>> if (skb->data_len > skb->end - skb->tail ||
>>>> - skb_cloned(skb))
>>>> + skb_cloned(skb) || is_ddp)
>>>> return;
>>>>
>>>> /* Nice, we can free page frag(s) right now */
>>>> diff --git a/net/ethtool/common.c b/net/ethtool/common.c
>>>> index 24036e3055a1..a2ff7a4a6bbf 100644
>>>> --- a/net/ethtool/common.c
>>>> +++ b/net/ethtool/common.c
>>>> @@ -68,6 +68,7 @@ const char netdev_features_strings[NETDEV_FEATURE_COUNT][ETH_GSTRING_LEN] = {
>>>> [NETIF_F_HW_TLS_RX_BIT] = "tls-hw-rx-offload",
>>>> [NETIF_F_GRO_FRAGLIST_BIT] = "rx-gro-list",
>>>> [NETIF_F_HW_MACSEC_BIT] = "macsec-hw-offload",
>>>> + [NETIF_F_HW_TCP_DDP_BIT] = "tcp-ddp-offload",
>>>> };
>>>>
>>>> const char
>>>> --
>>>> 2.24.1
>>>>
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