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

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Date: Tue, 26 Sep 2023 20:30:06 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Dust Li <dust.li@...ux.alibaba.com>
Cc: Alexandra Winter <wintera@...ux.ibm.com>,
	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 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