Re: [PATCH 1/4] sunrpc: flag transports as using IETF approved congestion control protocols

[Tom Talpey <tom@talpey.com>]

On 2/23/2017 3:00 PM, Jeff Layton wrote:
> On Thu, 2017-02-23 at 14:42 -0500, Tom Talpey 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.
>>
>> Net-net, inspecting only the RDMA attribute of the transport may be
>> insufficient here.
>>
>> 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.
>>
>
> (cc'ing Chuck and the linux-rdma list)
>
> Thanks Tom, that's very interesting.
>
> Not being well versed in the xprtrdma layer, what condition should we
> use here to set the flag? git grep shows that the string "ROCEV1" only
> shows up in the bxnt_en driver. Is there some way to determine this
> generically for any given RDMA driver?

I would not code RoCEv1 as an exception, I would code iWARP and RoCEv2
as the only eligible ones. There are any number of other possibilities,
none of which should be automatically flagged as congestion-controlled.

I'm also not sure I'm comfortable with hardcoding such a list into RPC.
But it may be the best you can do for now. Chuck, are you aware of a
verbs interface to obtain the RDMA transport type?

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);
>>>
>>>
>