Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:3 as permitted sender) client-ip=2620:137:e000::3:3;
Date:   Tue, 26 Sep 2023 20:09:03 +0800
From:   Dust Li <dust.li@linux.alibaba.com>
To:     Leon Romanovsky <leon@kernel.org>,
        Alexandra Winter <wintera@linux.ibm.com>
Cc:     Albert Huang <huangjie.albert@bytedance.com>,
        Karsten Graul <kgraul@linux.ibm.com>,
        Wenjia Zhang <wenjia@linux.ibm.com>,
        Jan Karcher <jaka@linux.ibm.com>,
        "D. Wythe" <alibuda@linux.alibaba.com>,
        Tony Lu <tonylu@linux.alibaba.com>,
        Wen Gu <guwen@linux.alibaba.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, linux-s390@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        RDMA mailing list <linux-rdma@vger.kernel.org>,
        Jason Gunthorpe <jgg@nvidia.com>
Subject: Re: [PATCH net-next] net/smc: add support for netdevice in
 containers.
Message-ID: <20230926120903.GD92403@linux.alibaba.com>
Reply-To: dust.li@linux.alibaba.com
References: <20230925023546.9964-1-huangjie.albert@bytedance.com>
 <20230926104831.GJ1642130@unreal>
 <76a74084-a900-d559-1f63-deff84e5848a@linux.ibm.com>
 <20230926114104.GL1642130@unreal>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230926114104.GL1642130@unreal>
Precedence: bulk

On Tue, Sep 26, 2023 at 02:41:04PM +0300, Leon Romanovsky wrote:
>On Tue, Sep 26, 2023 at 01:14:04PM +0200, Alexandra Winter wrote:
>> 
>> 
>> On 26.09.23 12:48, Leon Romanovsky wrote:
>> > This patch made me wonder, why doesn't SMC use RDMA-CM like all other
>> > in-kernel ULPs which work over RDMA?
>> > 
>> > Thanks
>> 
>> The idea behind SMC is that it should look an feel to the applications
>> like TCP sockets. So for connection management it uses TCP over IP;
>> RDMA is just used for the data transfer.
>
>I think that it is not different from other ULPs. For example, RDS works
>over sockets and doesn't touch or reimplement GID management logic.

I think the difference is SMC socket need to be compatible with TCP
socket, so it need a tcp socket to fallback when something is not working.

If SMC works with rdmacm, it still need a fallback-to-tcp socket, and
the tcp connection has to be established for each SMC socket before the
SMC socket got established, that would make rdmacm meaningless.

Best regards,
Dust

>
>Thanks