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Date: Sat, 9 Sep 2017 22:32:17 -0700
From: Tom Herbert <tom@...bertland.com>
To: Sridhar Samudrala <sridhar.samudrala@...el.com>
Cc: Alexander Duyck <alexander.h.duyck@...el.com>,
Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH] net: Introduce a socket option to enable picking tx
queue based on rx queue.
On Thu, Aug 31, 2017 at 4:27 PM, Sridhar Samudrala
<sridhar.samudrala@...el.com> wrote:
> This patch introduces a new socket option SO_SYMMETRIC_QUEUES that can be used
> to enable symmetric tx and rx queues on a socket.
>
> This option is specifically useful for epoll based multi threaded workloads
> where each thread handles packets received on a single RX queue . In this model,
> we have noticed that it helps to send the packets on the same TX queue
> corresponding to the queue-pair associated with the RX queue specifically when
> busy poll is enabled with epoll().
>
Please provide more details, test results on exactly how this helps.
Why would this better than than optimized XPS?
Thanks,
Tom
> Two new fields are added to struct sock_common to cache the last rx ifindex and
> the rx queue in the receive path of an SKB. __netdev_pick_tx() returns the cached
> rx queue when this option is enabled and the TX is happening on the same device.
>
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@...el.com>
> ---
> include/net/request_sock.h | 1 +
> include/net/sock.h | 17 +++++++++++++++++
> include/uapi/asm-generic/socket.h | 2 ++
> net/core/dev.c | 8 +++++++-
> net/core/sock.c | 10 ++++++++++
> net/ipv4/tcp_input.c | 1 +
> net/ipv4/tcp_ipv4.c | 1 +
> net/ipv4/tcp_minisocks.c | 1 +
> 8 files changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/request_sock.h b/include/net/request_sock.h
> index 23e2205..c3bc12e 100644
> --- a/include/net/request_sock.h
> +++ b/include/net/request_sock.h
> @@ -100,6 +100,7 @@ static inline struct sock *req_to_sk(struct request_sock *req)
> req_to_sk(req)->sk_prot = sk_listener->sk_prot;
> sk_node_init(&req_to_sk(req)->sk_node);
> sk_tx_queue_clear(req_to_sk(req));
> + req_to_sk(req)->sk_symmetric_queues = sk_listener->sk_symmetric_queues;
> req->saved_syn = NULL;
> refcount_set(&req->rsk_refcnt, 0);
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 03a3625..3421809 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -138,11 +138,14 @@ void SOCK_DEBUG(const struct sock *sk, const char *msg, ...)
> * @skc_node: main hash linkage for various protocol lookup tables
> * @skc_nulls_node: main hash linkage for TCP/UDP/UDP-Lite protocol
> * @skc_tx_queue_mapping: tx queue number for this connection
> + * @skc_rx_queue_mapping: rx queue number for this connection
> + * @skc_rx_ifindex: rx ifindex for this connection
> * @skc_flags: place holder for sk_flags
> * %SO_LINGER (l_onoff), %SO_BROADCAST, %SO_KEEPALIVE,
> * %SO_OOBINLINE settings, %SO_TIMESTAMPING settings
> * @skc_incoming_cpu: record/match cpu processing incoming packets
> * @skc_refcnt: reference count
> + * @skc_symmetric_queues: symmetric tx/rx queues
> *
> * This is the minimal network layer representation of sockets, the header
> * for struct sock and struct inet_timewait_sock.
> @@ -177,6 +180,7 @@ struct sock_common {
> unsigned char skc_reuseport:1;
> unsigned char skc_ipv6only:1;
> unsigned char skc_net_refcnt:1;
> + unsigned char skc_symmetric_queues:1;
> int skc_bound_dev_if;
> union {
> struct hlist_node skc_bind_node;
> @@ -214,6 +218,8 @@ struct sock_common {
> struct hlist_nulls_node skc_nulls_node;
> };
> int skc_tx_queue_mapping;
> + int skc_rx_queue_mapping;
> + int skc_rx_ifindex;
> union {
> int skc_incoming_cpu;
> u32 skc_rcv_wnd;
> @@ -324,6 +330,8 @@ struct sock {
> #define sk_nulls_node __sk_common.skc_nulls_node
> #define sk_refcnt __sk_common.skc_refcnt
> #define sk_tx_queue_mapping __sk_common.skc_tx_queue_mapping
> +#define sk_rx_queue_mapping __sk_common.skc_rx_queue_mapping
> +#define sk_rx_ifindex __sk_common.skc_rx_ifindex
>
> #define sk_dontcopy_begin __sk_common.skc_dontcopy_begin
> #define sk_dontcopy_end __sk_common.skc_dontcopy_end
> @@ -340,6 +348,7 @@ struct sock {
> #define sk_reuseport __sk_common.skc_reuseport
> #define sk_ipv6only __sk_common.skc_ipv6only
> #define sk_net_refcnt __sk_common.skc_net_refcnt
> +#define sk_symmetric_queues __sk_common.skc_symmetric_queues
> #define sk_bound_dev_if __sk_common.skc_bound_dev_if
> #define sk_bind_node __sk_common.skc_bind_node
> #define sk_prot __sk_common.skc_prot
> @@ -1676,6 +1685,14 @@ static inline int sk_tx_queue_get(const struct sock *sk)
> return sk ? sk->sk_tx_queue_mapping : -1;
> }
>
> +static inline void sk_mark_rx_queue(struct sock *sk, struct sk_buff *skb)
> +{
> + if (sk->sk_symmetric_queues) {
> + sk->sk_rx_ifindex = skb->skb_iif;
> + sk->sk_rx_queue_mapping = skb_get_rx_queue(skb);
> + }
> +}
> +
> static inline void sk_set_socket(struct sock *sk, struct socket *sock)
> {
> sk_tx_queue_clear(sk);
> diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
> index e47c9e4..f6b416e 100644
> --- a/include/uapi/asm-generic/socket.h
> +++ b/include/uapi/asm-generic/socket.h
> @@ -106,4 +106,6 @@
>
> #define SO_ZEROCOPY 60
>
> +#define SO_SYMMETRIC_QUEUES 61
> +
> #endif /* __ASM_GENERIC_SOCKET_H */
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 270b547..d96cda8 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3322,7 +3322,13 @@ static u16 __netdev_pick_tx(struct net_device *dev, struct sk_buff *skb)
>
> if (queue_index < 0 || skb->ooo_okay ||
> queue_index >= dev->real_num_tx_queues) {
> - int new_index = get_xps_queue(dev, skb);
> + int new_index = -1;
> +
> + if (sk && sk->sk_symmetric_queues && dev->ifindex == sk->sk_rx_ifindex)
> + new_index = sk->sk_rx_queue_mapping;
> +
> + if (new_index < 0 || new_index >= dev->real_num_tx_queues)
> + new_index = get_xps_queue(dev, skb);
>
> if (new_index < 0)
> new_index = skb_tx_hash(dev, skb);
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 9b7b6bb..3876cce 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1059,6 +1059,10 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
> sock_valbool_flag(sk, SOCK_ZEROCOPY, valbool);
> break;
>
> + case SO_SYMMETRIC_QUEUES:
> + sk->sk_symmetric_queues = valbool;
> + break;
> +
> default:
> ret = -ENOPROTOOPT;
> break;
> @@ -1391,6 +1395,10 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
> v.val = sock_flag(sk, SOCK_ZEROCOPY);
> break;
>
> + case SO_SYMMETRIC_QUEUES:
> + v.val = sk->sk_symmetric_queues;
> + break;
> +
> default:
> /* We implement the SO_SNDLOWAT etc to not be settable
> * (1003.1g 7).
> @@ -2738,6 +2746,8 @@ void sock_init_data(struct socket *sock, struct sock *sk)
> sk->sk_max_pacing_rate = ~0U;
> sk->sk_pacing_rate = ~0U;
> sk->sk_incoming_cpu = -1;
> + sk->sk_rx_ifindex = -1;
> + sk->sk_rx_queue_mapping = -1;
> /*
> * Before updating sk_refcnt, we must commit prior changes to memory
> * (Documentation/RCU/rculist_nulls.txt for details)
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index c5d7656..12381e0 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -6356,6 +6356,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
> tcp_rsk(req)->snt_isn = isn;
> tcp_rsk(req)->txhash = net_tx_rndhash();
> tcp_openreq_init_rwin(req, sk, dst);
> + sk_mark_rx_queue(req_to_sk(req), skb);
> if (!want_cookie) {
> tcp_reqsk_record_syn(sk, req, skb);
> fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc);
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index a63486a..82f9af4 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1450,6 +1450,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
>
> sock_rps_save_rxhash(sk, skb);
> sk_mark_napi_id(sk, skb);
> + sk_mark_rx_queue(sk, skb);
> if (dst) {
> if (inet_sk(sk)->rx_dst_ifindex != skb->skb_iif ||
> !dst->ops->check(dst, 0)) {
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index 188a6f3..2b5efd5 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -809,6 +809,7 @@ int tcp_child_process(struct sock *parent, struct sock *child,
>
> /* record NAPI ID of child */
> sk_mark_napi_id(child, skb);
> + sk_mark_rx_queue(child, skb);
>
> tcp_segs_in(tcp_sk(child), skb);
> if (!sock_owned_by_user(child)) {
> --
> 1.8.3.1
>
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