Re: [PATCH v1 7/7] sunrpc: Allow keepalive ping on a credit-full transport

[Anna Schumaker <schumaker.anna-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Chuck,

On 01/26/2017 12:56 PM, Chuck Lever wrote:
> Allow RPC-over-RDMA to send NULL pings even when the transport has
> hit its credit limit.
> 
> One credit is reserved. It may be used only to send a keepalive
> ping.
> 
> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> ---
>  include/linux/sunrpc/sched.h    |    2 ++
>  net/sunrpc/xprt.c               |    4 ++++
>  net/sunrpc/xprtrdma/transport.c |    4 +++-
>  net/sunrpc/xprtrdma/verbs.c     |   13 ++++++++-----
>  4 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/sunrpc/sched.h b/include/linux/sunrpc/sched.h
> index 7ba040c..a65278e 100644
> --- a/include/linux/sunrpc/sched.h
> +++ b/include/linux/sunrpc/sched.h
> @@ -127,6 +127,7 @@ struct rpc_task_setup {
>  #define RPC_TASK_TIMEOUT	0x1000		/* fail with ETIMEDOUT on timeout */
>  #define RPC_TASK_NOCONNECT	0x2000		/* return ENOTCONN if not connected */
>  #define RPC_TASK_NO_RETRANS_TIMEOUT	0x4000		/* wait forever for a reply */
> +#define RPC_TASK_PRIORITY	0x8000		/* skip congestion control */

This file also defines various RPC_PRIORITY_<whatever> values that get used for the task->tk_priority field.  I wonder if there is a better name for this flag that would help keep people from confusing the two later down the line, but I'm also struggling to come up with anything better.

Thoughts?
Anna

>  
>  #define RPC_IS_ASYNC(t)		((t)->tk_flags & RPC_TASK_ASYNC)
>  #define RPC_IS_SWAPPER(t)	((t)->tk_flags & RPC_TASK_SWAPPER)
> @@ -135,6 +136,7 @@ struct rpc_task_setup {
>  #define RPC_IS_SOFT(t)		((t)->tk_flags & (RPC_TASK_SOFT|RPC_TASK_TIMEOUT))
>  #define RPC_IS_SOFTCONN(t)	((t)->tk_flags & RPC_TASK_SOFTCONN)
>  #define RPC_WAS_SENT(t)		((t)->tk_flags & RPC_TASK_SENT)
> +#define RPC_HAS_PRIORITY(t)	((t)->tk_flags & RPC_TASK_PRIORITY)
>  
>  #define RPC_TASK_RUNNING	0
>  #define RPC_TASK_QUEUED		1
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index b530a28..e8b7b9f 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -392,6 +392,10 @@ static inline void xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *ta
>  {
>  	struct rpc_rqst *req = task->tk_rqstp;
>  
> +	if (RPC_HAS_PRIORITY(task)) {
> +		req->rq_cong = 0;
> +		return 1;
> +	}
>  	if (req->rq_cong)
>  		return 1;
>  	dprintk("RPC: %5u xprt_cwnd_limited cong = %lu cwnd = %lu\n",
> diff --git a/net/sunrpc/xprtrdma/transport.c b/net/sunrpc/xprtrdma/transport.c
> index f97c851..e43cc85 100644
> --- a/net/sunrpc/xprtrdma/transport.c
> +++ b/net/sunrpc/xprtrdma/transport.c
> @@ -538,7 +538,9 @@ static void rpcrdma_keepalive_release(void *calldata)
>  
>  	data = xprt_get(xprt);
>  	null_task = rpc_call_null_helper(task->tk_client, xprt, NULL,
> -					 RPC_TASK_SOFT | RPC_TASK_ASYNC,
> +					 RPC_TASK_SOFT |
> +					 RPC_TASK_ASYNC |
> +					 RPC_TASK_PRIORITY,
>  					 &rpcrdma_keepalive_call_ops, data);
>  	if (!IS_ERR(null_task))
>  		rpc_put_task(null_task);
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index 7e14b73..3e218dd 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -136,19 +136,20 @@
>  static void
>  rpcrdma_update_granted_credits(struct rpcrdma_rep *rep)
>  {
> -	struct rpcrdma_msg *rmsgp = rdmab_to_msg(rep->rr_rdmabuf);
>  	struct rpcrdma_buffer *buffer = &rep->rr_rxprt->rx_buf;
> +	__be32 *p = rep->rr_rdmabuf->rg_base;
>  	u32 credits;
>  
>  	if (rep->rr_len < RPCRDMA_HDRLEN_ERR)
>  		return;
>  
> -	credits = be32_to_cpu(rmsgp->rm_credit);
> +	credits = be32_to_cpup(p + 2);
> +	if (credits > buffer->rb_max_requests)
> +		credits = buffer->rb_max_requests;
> +	/* Reserve one credit for keepalive ping */
> +	credits--;
>  	if (credits == 0)
>  		credits = 1;	/* don't deadlock */
> -	else if (credits > buffer->rb_max_requests)
> -		credits = buffer->rb_max_requests;
> -
>  	atomic_set(&buffer->rb_credits, credits);
>  }
>  
> @@ -914,6 +915,8 @@ struct rpcrdma_rep *
>  	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
>  	int i, rc;
>  
> +	if (r_xprt->rx_data.max_requests < 2)
> +		return -EINVAL;
>  	buf->rb_max_requests = r_xprt->rx_data.max_requests;
>  	buf->rb_bc_srv_max_requests = 0;
>  	atomic_set(&buf->rb_credits, 1);
> 
> --
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