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Subject: Re: [PATCH 1/4] sunrpc: flag transports as using IETF approved congestion control protocols
From: Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <2152dfdf-f847-2511-1600-6499b6ea9708@talpey.com>
Date: Thu, 23 Feb 2017 15:15:49 -0500
Cc: Jeff Layton <jlayton@redhat.com>, bfields@fieldses.org,
        trond.myklebust@primarydata.com, schumaker.anna@gmail.com,
        linux-nfs@vger.kernel.org
Message-Id: <01E75F0A-6F57-41B3-9C59-7CAED613D151@oracle.com>
References: <20170223170337.10686-1-jlayton@redhat.com> <20170223170337.10686-2-jlayton@redhat.com> <2152dfdf-f847-2511-1600-6499b6ea9708@talpey.com>
To: Tom Talpey <tom@talpey.com>
Sender: linux-nfs-owner@vger.kernel.org


--
Chuck Lever

> On Feb 23, 2017, at 2:42 PM, Tom Talpey <tom@talpey.com> wrote:
> 
>> On 2/23/2017 12:03 PM, Jeff Layton wrote:
>> Signed-off-by: Jeff Layton <jlayton@redhat.com>
>> ---
>> include/linux/sunrpc/svc_xprt.h          | 1 +
>> net/sunrpc/svcsock.c                     | 1 +
>> net/sunrpc/xprtrdma/svc_rdma_transport.c | 2 ++
> 
> There's a possibly-important detail here. Not all RDMA transports have
> "IETF-approved congestion control", for example, RoCEv1. However, iWARP
> and (arguably) RoCEv2 do. On the other hand, as a nonroutable protocol,
> RoCEv1 may not fall under this restriction.

Probably a discussion that could be handled in rfc5667bis. But it's
not clear what IETF-approved congestion control is, precisely.

We'd have to say something about InfiniBand (a transport which
is not specified by the IETF) too.


> Net-net, inspecting only the RDMA attribute of the transport may be
> insufficient here.

The transport implementation would have to set it in the svc_xprt
rather than having it be a constant field in the xprt class.


> It could be argued however that the xprtrdma layer, with its rpcrdma
> crediting, provides such congestion. But that needs to be made
> explicit, and perhaps, discussed in IETF. Initially, I think it would
> be important to flag this as a point for the future. For now, it may
> be best to flag RoCEv1 as not supporting congestion.
> 
> Tom.
> 
>> 3 files changed, 4 insertions(+)
>> 
>> diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
>> index 7440290f64ac..f8aa9452b63c 100644
>> --- a/include/linux/sunrpc/svc_xprt.h
>> +++ b/include/linux/sunrpc/svc_xprt.h
>> @@ -67,6 +67,7 @@ struct svc_xprt {
>> #define XPT_CACHE_AUTH    11        /* cache auth info */
>> #define XPT_LOCAL    12        /* connection from loopback interface */
>> #define XPT_KILL_TEMP   13        /* call xpo_kill_temp_xprt before closing */
>> +#define XPT_CONG_CTRL    14        /* IETF approved congestion control protocol */
>> 
>>    struct svc_serv        *xpt_server;    /* service for transport */
>>    atomic_t                xpt_reserved;    /* space on outq that is rsvd */
>> diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
>> index de066acdb34e..1956b8b96b2d 100644
>> --- a/net/sunrpc/svcsock.c
>> +++ b/net/sunrpc/svcsock.c
>> @@ -1306,6 +1306,7 @@ static void svc_tcp_init(struct svc_sock *svsk, struct svc_serv *serv)
>>    svc_xprt_init(sock_net(svsk->sk_sock->sk), &svc_tcp_class,
>>              &svsk->sk_xprt, serv);
>>    set_bit(XPT_CACHE_AUTH, &svsk->sk_xprt.xpt_flags);
>> +    set_bit(XPT_CONG_CTRL, &svsk->sk_xprt.xpt_flags);
>>    if (sk->sk_state == TCP_LISTEN) {
>>        dprintk("setting up TCP socket for listening\n");
>>        set_bit(XPT_LISTENER, &svsk->sk_xprt.xpt_flags);
>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> index 39652d390a9c..96b4797c2c54 100644
>> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> @@ -571,6 +571,8 @@ static struct svcxprt_rdma *rdma_create_xprt(struct svc_serv *serv,
>>    spin_lock_init(&cma_xprt->sc_ctxt_lock);
>>    spin_lock_init(&cma_xprt->sc_map_lock);
>> 
>> +    set_bit(XPT_CONG_CTRL, &cma_xprt->sc_xprt.xpt_flags);
>> +
>>    if (listener)
>>        set_bit(XPT_LISTENER, &cma_xprt->sc_xprt.xpt_flags);
>> 
>> 
> --
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