On Thu, Jan 27, 2022 at 08:08:03PM +0800, D. Wythe wrote: > 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..1903927 100644 > --- a/net/smc/Kconfig > +++ b/net/smc/Kconfig > @@ -19,3 +19,15 @@ config SMC_DIAG > smcss. > > if unsure, say Y. > + > +if MPTCP If we really need MPTCP? According the context, this doesn't seem necessary. > + > +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 Consider using a dynamic switch to enable or disable this feature? SMC currently have netlink interface in smc_netlink.c, we can extend this in userspace tool smc-tools. Thank you, Tony Lu
