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Date:   Tue, 26 Sep 2023 20:30:06 +0300
From:   Leon Romanovsky <leon@kernel.org>
To:     Dust Li <dust.li@linux.alibaba.com>
Cc:     Alexandra Winter <wintera@linux.ibm.com>,
        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: <20230926173006.GN1642130@unreal>
References: <20230925023546.9964-1-huangjie.albert@bytedance.com>
 <20230926104831.GJ1642130@unreal>
 <76a74084-a900-d559-1f63-deff84e5848a@linux.ibm.com>
 <20230926114104.GL1642130@unreal>
 <20230926120903.GD92403@linux.alibaba.com>
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On Tue, Sep 26, 2023 at 08:09:03PM +0800, Dust Li wrote:
> 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.

You still need to perform device-GID-route translations [1], which sounds
to me very RDMA-CM. I'm not asking you to rewrite the code, but trying
to get rationale behind reimplementing part of RDMA subsystem.

Thanks

[1] 24fb68111d45 ("net/smc: retrieve v2 gid from IB device")

> 
> Best regards,
> Dust
> 
> >
> >Thanks