linux-kernel - Re: [PATCH net-next] net/smc: add support for netdevice in containers.

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Message-ID: <20230926120903.GD92403@linux.alibaba.com>
Date:   Tue, 26 Sep 2023 20:09:03 +0800
From:   Dust Li <dust.li@...ux.alibaba.com>
To:     Leon Romanovsky <leon@...nel.org>,
        Alexandra Winter <wintera@...ux.ibm.com>
Cc:     Albert Huang <huangjie.albert@...edance.com>,
        Karsten Graul <kgraul@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Jan Karcher <jaka@...ux.ibm.com>,
        "D. Wythe" <alibuda@...ux.alibaba.com>,
        Tony Lu <tonylu@...ux.alibaba.com>,
        Wen Gu <guwen@...ux.alibaba.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-s390@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH net-next] net/smc: add support for netdevice in
 containers.

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