Date:   Mon, 1 May 2017 17:55:06 +0000
From:   Parav Pandit <parav@...lanox.com>
To:     Bart Van Assche <Bart.VanAssche@...disk.com>,
        "hch@....de" <hch@....de>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "ubraun@...ux.vnet.ibm.com" <ubraun@...ux.vnet.ibm.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: RE: net/smc and the RDMA core

Hi Bart, Ursula, Dave,

I am particularly concerned about SMC as address family.
It should not be treated as address family, but rather an additional protocol similar for socket type SOCK_STREAM.
While doing performance benchmarking last month and while porting few database application,

I encountered a major hurdle where user space library heavily depend on AF_INET and AF_INET6 family through get_addrinfo and other friend functions.
Adding or treating AF_SMC as AF_INET just doesn't sound right.

Most user space code doesn't care for the protocol field, but do handle domain field.

I personally believe it's not too late to modify SMC to drop expose AF_SMC and have it exposed through new protocol that can be exposed through socket() API.

Parav

> -----Original Message-----
> From: linux-rdma-owner@...r.kernel.org [mailto:linux-rdma-
> owner@...r.kernel.org] On Behalf Of Bart Van Assche
> Sent: Monday, May 1, 2017 12:30 PM
> To: hch@....de; davem@...emloft.net; ubraun@...ux.vnet.ibm.com
> Cc: netdev@...r.kernel.org; linux-rdma@...r.kernel.org
> Subject: Re: net/smc and the RDMA core
> 
> On Mon, 2017-05-01 at 18:33 +0200, Christoph Hellwig wrote:
> > Hi Ursual, hi netdev reviewers,
> >
> > how did the smc protocol manage to get merged without any review on
> > linux-rdma at all?  As the results it seems it's very substandard in
> > terms of RDMA API usage, e.g. it neither uses the proper CQ API nor
> > the RDMA R/W API, and other will probably find additional issues as
> > well.
> 
> Hello Dave and Ursula,
> 
> It seems very rude to me to have merged the SMC protocol driver without
> having involved the linux-rdma community. Anyway, I have the following
> questions for Dave and Ursula:
> * Since the Linux kernel is standards based: where can we find the standard
>   that defines the SMC wire protocol? If this protocol has not been
>   standardized yet: in what file (other than *.[ch]) in the Linux kernel
>   tree has this protocol been documented?
> * What are the differences between the SMC protocol, the SDP protocol and
>   the rsockets protocol? How do existing implementations for these protocols
>   compare to each other from a performance point of view? If no performance
>   comparison between these protocols is available, shouldn't the performance
>   of these protocols have been compared with each other before a review of
>   the SMC driver even started?
> * What are the reasons why the SDP driver was never accepted upstream? Do
>   the arguments why SDP was not accepted upstream also apply to the SMC
>   driver (SDP = Sockets Direct Protocol)?
> * Since SMC has to be selected by specifying AF_SMC, how are users expected
>   to specify whether AF_INET, AF_INET6 or yet another address family should
>   be used to set up a connection between SMC endpoints?
> * Is the SMC driver limited to RoCE? Are you aware that the rsockets library
>   supports multiple transport layers (RoCE, IB and iWARP)?
> * Since functionality that is similar what the SMC driver provides already
>   exists in user space (rsockets), why has this functionality been
>   reimplemented as a kernel driver (SMC)?
> 
> Bart.--
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