From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F0D36C433EF for ; Fri, 28 Jan 2022 07:17:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346767AbiA1HRr (ORCPT ); Fri, 28 Jan 2022 02:17:47 -0500 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:55965 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242865AbiA1HRl (ORCPT ); Fri, 28 Jan 2022 02:17:41 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R281e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04395;MF=tonylu@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0V31PeLV_1643354258; Received: from localhost(mailfrom:tonylu@linux.alibaba.com fp:SMTPD_---0V31PeLV_1643354258) by smtp.aliyun-inc.com(127.0.0.1); Fri, 28 Jan 2022 15:17:38 +0800 Date: Fri, 28 Jan 2022 15:17:37 +0800 From: Tony Lu To: "D. Wythe" Cc: kgraul@linux.ibm.com, kuba@kernel.org, davem@davemloft.net, netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-rdma@vger.kernel.org Subject: Re: [PATCH net-next 3/3] net/smc: Fallback when handshake workqueue congested Message-ID: Reply-To: Tony Lu References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Thu, Jan 27, 2022 at 08:08:03PM +0800, D. Wythe wrote: > From: "D. Wythe" > > 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@linux.alibaba.com/ > Signed-off-by: D. Wythe > --- > 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