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

Chuck Lever
2017-02-23T20:17:16Z

--
Chuck Lever

> On Feb 23, 2017, at 3:06 PM, Tom Talpey <tom-CLs1Zie5N5HQT0dZR+AlfA@public.gmane.org> wrote:
>
>> 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-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>>>> ---
>>>> 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?

Yes, I can have a look when I get to Connectathon.

>
> 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);
>>>>
>>>>
>>