From: "D. Wythe" <alibuda@xxxxxxxxxxxxxxxxx> This patch intends to provide a mechanism to allow automatic fallback to TCP according to the pressure of SMC handshake process. At present, frequent visits will cause the incoming connections to be backlogged in SMC handshake queue, raise the connections established time. Which is quite unacceptable for those applications who base on short lived connections. It should be optional for applications that don't care about connection established time. For now, this patch only provides the switch at the compile time. There are two ways to implement this mechanism: 1. Fallback when TCP established. 2. Fallback before TCP established. In the first way, we need to wait and receive CLC messages that the client will potentially send, and then actively reply with a decline message, in a sense, which is also a sort of SMC handshake, affect the connections established time on its way. In the second way, the only problem is that we need to inject SMC logic into TCP when it is about to reply the incoming SYN, since we already do that, it's seems not a problem anymore. And advantage is obvious, few additional processes are required to complete the fallback. This patch use the second way. Link: https://lore.kernel.org/all/1641301961-59331-1-git-send-email-alibuda@xxxxxxxxxxxxxxxxx/ Signed-off-by: D. Wythe <alibuda@xxxxxxxxxxxxxxxxx> --- include/linux/tcp.h | 1 + net/ipv4/tcp_input.c | 3 ++- net/smc/Kconfig | 12 ++++++++++++ net/smc/af_smc.c | 22 ++++++++++++++++++++++ 4 files changed, 37 insertions(+), 1 deletion(-) diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 78b91bb..1c4ae5d 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -394,6 +394,7 @@ struct tcp_sock { bool is_mptcp; #endif #if IS_ENABLED(CONFIG_SMC) + bool (*smc_in_limited)(const struct sock *sk); bool syn_smc; /* SYN includes SMC */ #endif diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index dc49a3d..9890de9 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -6701,7 +6701,8 @@ static void tcp_openreq_init(struct request_sock *req, ireq->ir_num = ntohs(tcp_hdr(skb)->dest); ireq->ir_mark = inet_request_mark(sk, skb); #if IS_ENABLED(CONFIG_SMC) - ireq->smc_ok = rx_opt->smc_ok; + ireq->smc_ok = rx_opt->smc_ok && !(tcp_sk(sk)->smc_in_limited && + tcp_sk(sk)->smc_in_limited(sk)); #endif } diff --git a/net/smc/Kconfig b/net/smc/Kconfig index 1ab3c5a..a4e1713 100644 --- a/net/smc/Kconfig +++ b/net/smc/Kconfig @@ -19,3 +19,15 @@ config SMC_DIAG smcss. if unsure, say Y. + +if SMC + +config SMC_AUTO_FALLBACK + bool "SMC: automatic fallback to TCP" + default y + help + Allow automatic fallback to TCP accroding to the pressure of SMC-R + handshake process. + + If that's not what you except or unsure, say N. +endif diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c index 66a0e64..49b8a29 100644 --- a/net/smc/af_smc.c +++ b/net/smc/af_smc.c @@ -101,6 +101,24 @@ static struct sock *smc_tcp_syn_recv_sock(const struct sock *sk, struct sk_buff return NULL; } +#if IS_ENABLED(CONFIG_SMC_AUTO_FALLBACK) +static bool smc_is_in_limited(const struct sock *sk) +{ + const struct smc_sock *smc; + + smc = (const struct smc_sock *) + ((uintptr_t)sk->sk_user_data & ~SK_USER_DATA_NOCOPY); + + if (!smc) + return true; + + if (workqueue_congested(WORK_CPU_UNBOUND, smc_hs_wq)) + return true; + + return false; +} +#endif + static struct smc_hashinfo smc_v4_hashinfo = { .lock = __RW_LOCK_UNLOCKED(smc_v4_hashinfo.lock), }; @@ -2206,6 +2224,10 @@ static int smc_listen(struct socket *sock, int backlog) inet_csk(smc->clcsock->sk)->icsk_af_ops = &smc->af_ops; +#if IS_ENABLED(CONFIG_SMC_AUTO_FALLBACK) + tcp_sk(smc->clcsock->sk)->smc_in_limited = smc_is_in_limited; +#endif + rc = kernel_listen(smc->clcsock, backlog); if (rc) { smc->clcsock->sk->sk_data_ready = smc->clcsk_data_ready; -- 1.8.3.1
