[v1,08/20] xprtrdma: Move credit update to RPC reply handler
diff mbox

Message ID 20150107231252.13466.53108.stgit@manet.1015granger.net
State New, archived
Headers show

Commit Message

Chuck Lever Jan. 7, 2015, 11:12 p.m. UTC
Reduce work in the receive CQ handler, which is run at hardware
interrupt level, by moving the RPC/RDMA credit update logic to the
RPC reply handler.

This has some additional benefits: More header sanity checking is
done before trusting the incoming credit value, and the receive CQ
handler no longer touches the RPC/RDMA header. Finally, no longer
any need to update and read rb_credits atomically, so the rb_credits
field can be removed.

This further extends work begun by commit e7ce710a8802 ("xprtrdma:
Avoid deadlock when credit window is reset").

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xprtrdma/rpc_rdma.c  |   10 ++++++++--
 net/sunrpc/xprtrdma/verbs.c     |   15 ++-------------
 net/sunrpc/xprtrdma/xprt_rdma.h |    1 -
 3 files changed, 10 insertions(+), 16 deletions(-)


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Comments

Schumaker, Anna Jan. 8, 2015, 3:53 p.m. UTC | #1
Hey Chuck,

On 01/07/2015 06:12 PM, Chuck Lever wrote:
> Reduce work in the receive CQ handler, which is run at hardware
> interrupt level, by moving the RPC/RDMA credit update logic to the
> RPC reply handler.
> 
> This has some additional benefits: More header sanity checking is
> done before trusting the incoming credit value, and the receive CQ
> handler no longer touches the RPC/RDMA header. Finally, no longer
> any need to update and read rb_credits atomically, so the rb_credits
> field can be removed.
> 
> This further extends work begun by commit e7ce710a8802 ("xprtrdma:
> Avoid deadlock when credit window is reset").
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/sunrpc/xprtrdma/rpc_rdma.c  |   10 ++++++++--
>  net/sunrpc/xprtrdma/verbs.c     |   15 ++-------------
>  net/sunrpc/xprtrdma/xprt_rdma.h |    1 -
>  3 files changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
> index dcf5ebc..d731010 100644
> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
> @@ -736,7 +736,7 @@ rpcrdma_reply_handler(struct rpcrdma_rep *rep)
>  	struct rpc_xprt *xprt = rep->rr_xprt;
>  	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
>  	__be32 *iptr;
> -	int rdmalen, status;
> +	int credits, rdmalen, status;
>  	unsigned long cwnd;
>  
>  	/* Check status. If bad, signal disconnect and return rep to pool */
> @@ -871,8 +871,14 @@ badheader:
>  		break;
>  	}
>  
> +	credits = be32_to_cpu(headerp->rm_credit);
> +	if (credits == 0)
> +		credits = 1;	/* don't deadlock */
> +	else if (credits > r_xprt->rx_buf.rb_max_requests)
> +		credits = r_xprt->rx_buf.rb_max_requests;

Can rb_max_requests ever drop to 0?

Anna

> +
>  	cwnd = xprt->cwnd;
> -	xprt->cwnd = atomic_read(&r_xprt->rx_buf.rb_credits) << RPC_CWNDSHIFT;
> +	xprt->cwnd = credits << RPC_CWNDSHIFT;
>  	if (xprt->cwnd > cwnd)
>  		xprt_release_rqst_cong(rqst->rq_task);
>  
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index 1000f63..71a071a 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -49,6 +49,7 @@
>  
>  #include <linux/interrupt.h>
>  #include <linux/slab.h>
> +#include <linux/prefetch.h>
>  #include <asm/bitops.h>
>  
>  #include "xprt_rdma.h"
> @@ -298,17 +299,7 @@ rpcrdma_recvcq_process_wc(struct ib_wc *wc, struct list_head *sched_list)
>  	rep->rr_len = wc->byte_len;
>  	ib_dma_sync_single_for_cpu(rdmab_to_ia(rep->rr_buffer)->ri_id->device,
>  			rep->rr_iov.addr, rep->rr_len, DMA_FROM_DEVICE);
> -
> -	if (rep->rr_len >= 16) {
> -		struct rpcrdma_msg *p = (struct rpcrdma_msg *)rep->rr_base;
> -		unsigned int credits = ntohl(p->rm_credit);
> -
> -		if (credits == 0)
> -			credits = 1;	/* don't deadlock */
> -		else if (credits > rep->rr_buffer->rb_max_requests)
> -			credits = rep->rr_buffer->rb_max_requests;
> -		atomic_set(&rep->rr_buffer->rb_credits, credits);
> -	}
> +	prefetch(rep->rr_base);
>  
>  out_schedule:
>  	list_add_tail(&rep->rr_list, sched_list);
> @@ -480,7 +471,6 @@ rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
>  	case RDMA_CM_EVENT_DEVICE_REMOVAL:
>  		connstate = -ENODEV;
>  connected:
> -		atomic_set(&rpcx_to_rdmax(ep->rep_xprt)->rx_buf.rb_credits, 1);
>  		dprintk("RPC:       %s: %sconnected\n",
>  					__func__, connstate > 0 ? "" : "dis");
>  		ep->rep_connected = connstate;
> @@ -1186,7 +1176,6 @@ rpcrdma_buffer_create(struct rpcrdma_buffer *buf, struct rpcrdma_ep *ep,
>  
>  	buf->rb_max_requests = cdata->max_requests;
>  	spin_lock_init(&buf->rb_lock);
> -	atomic_set(&buf->rb_credits, 1);
>  
>  	/* Need to allocate:
>  	 *   1.  arrays for send and recv pointers
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index 532d586..3fcc92b 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -248,7 +248,6 @@ struct rpcrdma_req {
>   */
>  struct rpcrdma_buffer {
>  	spinlock_t	rb_lock;	/* protects indexes */
> -	atomic_t	rb_credits;	/* most recent server credits */
>  	int		rb_max_requests;/* client max requests */
>  	struct list_head rb_mws;	/* optional memory windows/fmrs/frmrs */
>  	struct list_head rb_all;
> 
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> 

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Chuck Lever Jan. 8, 2015, 4:10 p.m. UTC | #2
On Jan 8, 2015, at 10:53 AM, Anna Schumaker <Anna.Schumaker@netapp.com> wrote:

> Hey Chuck,
> 
> On 01/07/2015 06:12 PM, Chuck Lever wrote:
>> Reduce work in the receive CQ handler, which is run at hardware
>> interrupt level, by moving the RPC/RDMA credit update logic to the
>> RPC reply handler.
>> 
>> This has some additional benefits: More header sanity checking is
>> done before trusting the incoming credit value, and the receive CQ
>> handler no longer touches the RPC/RDMA header. Finally, no longer
>> any need to update and read rb_credits atomically, so the rb_credits
>> field can be removed.
>> 
>> This further extends work begun by commit e7ce710a8802 ("xprtrdma:
>> Avoid deadlock when credit window is reset").
>> 
>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>> ---
>> net/sunrpc/xprtrdma/rpc_rdma.c  |   10 ++++++++--
>> net/sunrpc/xprtrdma/verbs.c     |   15 ++-------------
>> net/sunrpc/xprtrdma/xprt_rdma.h |    1 -
>> 3 files changed, 10 insertions(+), 16 deletions(-)
>> 
>> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
>> index dcf5ebc..d731010 100644
>> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
>> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
>> @@ -736,7 +736,7 @@ rpcrdma_reply_handler(struct rpcrdma_rep *rep)
>> 	struct rpc_xprt *xprt = rep->rr_xprt;
>> 	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
>> 	__be32 *iptr;
>> -	int rdmalen, status;
>> +	int credits, rdmalen, status;
>> 	unsigned long cwnd;
>> 
>> 	/* Check status. If bad, signal disconnect and return rep to pool */
>> @@ -871,8 +871,14 @@ badheader:
>> 		break;
>> 	}
>> 
>> +	credits = be32_to_cpu(headerp->rm_credit);
>> +	if (credits == 0)
>> +		credits = 1;	/* don't deadlock */
>> +	else if (credits > r_xprt->rx_buf.rb_max_requests)
>> +		credits = r_xprt->rx_buf.rb_max_requests;
> 
> Can rb_max_requests ever drop to 0?

rb_max_requests is set at mount time to xprt_rdma_slot_table_entries.
rb_max_requests is not changed again.

xprt_rdma_slot_table_entries is set to a compile-time constant,
but can be changed via a /proc file setting. The lower and upper
bounds are min_slot_table_size and max_slot_table_size, both set
to compile-time constants.

IMO there’s no practical danger rb_max_requests will ever be zero
unless someone makes a coding mistake.

Did you want me to reverse the order of the if conditions as a
defensive coding measure?


> Anna
> 
>> +
>> 	cwnd = xprt->cwnd;
>> -	xprt->cwnd = atomic_read(&r_xprt->rx_buf.rb_credits) << RPC_CWNDSHIFT;
>> +	xprt->cwnd = credits << RPC_CWNDSHIFT;
>> 	if (xprt->cwnd > cwnd)
>> 		xprt_release_rqst_cong(rqst->rq_task);
>> 
>> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
>> index 1000f63..71a071a 100644
>> --- a/net/sunrpc/xprtrdma/verbs.c
>> +++ b/net/sunrpc/xprtrdma/verbs.c
>> @@ -49,6 +49,7 @@
>> 
>> #include <linux/interrupt.h>
>> #include <linux/slab.h>
>> +#include <linux/prefetch.h>
>> #include <asm/bitops.h>
>> 
>> #include "xprt_rdma.h"
>> @@ -298,17 +299,7 @@ rpcrdma_recvcq_process_wc(struct ib_wc *wc, struct list_head *sched_list)
>> 	rep->rr_len = wc->byte_len;
>> 	ib_dma_sync_single_for_cpu(rdmab_to_ia(rep->rr_buffer)->ri_id->device,
>> 			rep->rr_iov.addr, rep->rr_len, DMA_FROM_DEVICE);
>> -
>> -	if (rep->rr_len >= 16) {
>> -		struct rpcrdma_msg *p = (struct rpcrdma_msg *)rep->rr_base;
>> -		unsigned int credits = ntohl(p->rm_credit);
>> -
>> -		if (credits == 0)
>> -			credits = 1;	/* don't deadlock */
>> -		else if (credits > rep->rr_buffer->rb_max_requests)
>> -			credits = rep->rr_buffer->rb_max_requests;
>> -		atomic_set(&rep->rr_buffer->rb_credits, credits);
>> -	}
>> +	prefetch(rep->rr_base);
>> 
>> out_schedule:
>> 	list_add_tail(&rep->rr_list, sched_list);
>> @@ -480,7 +471,6 @@ rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
>> 	case RDMA_CM_EVENT_DEVICE_REMOVAL:
>> 		connstate = -ENODEV;
>> connected:
>> -		atomic_set(&rpcx_to_rdmax(ep->rep_xprt)->rx_buf.rb_credits, 1);
>> 		dprintk("RPC:       %s: %sconnected\n",
>> 					__func__, connstate > 0 ? "" : "dis");
>> 		ep->rep_connected = connstate;
>> @@ -1186,7 +1176,6 @@ rpcrdma_buffer_create(struct rpcrdma_buffer *buf, struct rpcrdma_ep *ep,
>> 
>> 	buf->rb_max_requests = cdata->max_requests;
>> 	spin_lock_init(&buf->rb_lock);
>> -	atomic_set(&buf->rb_credits, 1);
>> 
>> 	/* Need to allocate:
>> 	 *   1.  arrays for send and recv pointers
>> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
>> index 532d586..3fcc92b 100644
>> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
>> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
>> @@ -248,7 +248,6 @@ struct rpcrdma_req {
>>  */
>> struct rpcrdma_buffer {
>> 	spinlock_t	rb_lock;	/* protects indexes */
>> -	atomic_t	rb_credits;	/* most recent server credits */
>> 	int		rb_max_requests;/* client max requests */
>> 	struct list_head rb_mws;	/* optional memory windows/fmrs/frmrs */
>> 	struct list_head rb_all;
>> 
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> 
> 

--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com



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Schumaker, Anna Jan. 8, 2015, 5:49 p.m. UTC | #3
On 01/08/2015 11:10 AM, Chuck Lever wrote:
> 
> On Jan 8, 2015, at 10:53 AM, Anna Schumaker <Anna.Schumaker@netapp.com> wrote:
> 
>> Hey Chuck,
>>
>> On 01/07/2015 06:12 PM, Chuck Lever wrote:
>>> Reduce work in the receive CQ handler, which is run at hardware
>>> interrupt level, by moving the RPC/RDMA credit update logic to the
>>> RPC reply handler.
>>>
>>> This has some additional benefits: More header sanity checking is
>>> done before trusting the incoming credit value, and the receive CQ
>>> handler no longer touches the RPC/RDMA header. Finally, no longer
>>> any need to update and read rb_credits atomically, so the rb_credits
>>> field can be removed.
>>>
>>> This further extends work begun by commit e7ce710a8802 ("xprtrdma:
>>> Avoid deadlock when credit window is reset").
>>>
>>> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
>>> ---
>>> net/sunrpc/xprtrdma/rpc_rdma.c  |   10 ++++++++--
>>> net/sunrpc/xprtrdma/verbs.c     |   15 ++-------------
>>> net/sunrpc/xprtrdma/xprt_rdma.h |    1 -
>>> 3 files changed, 10 insertions(+), 16 deletions(-)
>>>
>>> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
>>> index dcf5ebc..d731010 100644
>>> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
>>> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
>>> @@ -736,7 +736,7 @@ rpcrdma_reply_handler(struct rpcrdma_rep *rep)
>>> 	struct rpc_xprt *xprt = rep->rr_xprt;
>>> 	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
>>> 	__be32 *iptr;
>>> -	int rdmalen, status;
>>> +	int credits, rdmalen, status;
>>> 	unsigned long cwnd;
>>>
>>> 	/* Check status. If bad, signal disconnect and return rep to pool */
>>> @@ -871,8 +871,14 @@ badheader:
>>> 		break;
>>> 	}
>>>
>>> +	credits = be32_to_cpu(headerp->rm_credit);
>>> +	if (credits == 0)
>>> +		credits = 1;	/* don't deadlock */
>>> +	else if (credits > r_xprt->rx_buf.rb_max_requests)
>>> +		credits = r_xprt->rx_buf.rb_max_requests;
>>
>> Can rb_max_requests ever drop to 0?
> 
> rb_max_requests is set at mount time to xprt_rdma_slot_table_entries.
> rb_max_requests is not changed again.
> 
> xprt_rdma_slot_table_entries is set to a compile-time constant,
> but can be changed via a /proc file setting. The lower and upper
> bounds are min_slot_table_size and max_slot_table_size, both set
> to compile-time constants.
> 
> IMO there?s no practical danger rb_max_requests will ever be zero
> unless someone makes a coding mistake.
> 
> Did you want me to reverse the order of the if conditions as a
> defensive coding measure?

If there is no practical danger then it's probably fine the way it is.  Thanks for double checking!

Anna
> 
> 
>> Anna
>>
>>> +
>>> 	cwnd = xprt->cwnd;
>>> -	xprt->cwnd = atomic_read(&r_xprt->rx_buf.rb_credits) << RPC_CWNDSHIFT;
>>> +	xprt->cwnd = credits << RPC_CWNDSHIFT;
>>> 	if (xprt->cwnd > cwnd)
>>> 		xprt_release_rqst_cong(rqst->rq_task);
>>>
>>> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
>>> index 1000f63..71a071a 100644
>>> --- a/net/sunrpc/xprtrdma/verbs.c
>>> +++ b/net/sunrpc/xprtrdma/verbs.c
>>> @@ -49,6 +49,7 @@
>>>
>>> #include <linux/interrupt.h>
>>> #include <linux/slab.h>
>>> +#include <linux/prefetch.h>
>>> #include <asm/bitops.h>
>>>
>>> #include "xprt_rdma.h"
>>> @@ -298,17 +299,7 @@ rpcrdma_recvcq_process_wc(struct ib_wc *wc, struct list_head *sched_list)
>>> 	rep->rr_len = wc->byte_len;
>>> 	ib_dma_sync_single_for_cpu(rdmab_to_ia(rep->rr_buffer)->ri_id->device,
>>> 			rep->rr_iov.addr, rep->rr_len, DMA_FROM_DEVICE);
>>> -
>>> -	if (rep->rr_len >= 16) {
>>> -		struct rpcrdma_msg *p = (struct rpcrdma_msg *)rep->rr_base;
>>> -		unsigned int credits = ntohl(p->rm_credit);
>>> -
>>> -		if (credits == 0)
>>> -			credits = 1;	/* don't deadlock */
>>> -		else if (credits > rep->rr_buffer->rb_max_requests)
>>> -			credits = rep->rr_buffer->rb_max_requests;
>>> -		atomic_set(&rep->rr_buffer->rb_credits, credits);
>>> -	}
>>> +	prefetch(rep->rr_base);
>>>
>>> out_schedule:
>>> 	list_add_tail(&rep->rr_list, sched_list);
>>> @@ -480,7 +471,6 @@ rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
>>> 	case RDMA_CM_EVENT_DEVICE_REMOVAL:
>>> 		connstate = -ENODEV;
>>> connected:
>>> -		atomic_set(&rpcx_to_rdmax(ep->rep_xprt)->rx_buf.rb_credits, 1);
>>> 		dprintk("RPC:       %s: %sconnected\n",
>>> 					__func__, connstate > 0 ? "" : "dis");
>>> 		ep->rep_connected = connstate;
>>> @@ -1186,7 +1176,6 @@ rpcrdma_buffer_create(struct rpcrdma_buffer *buf, struct rpcrdma_ep *ep,
>>>
>>> 	buf->rb_max_requests = cdata->max_requests;
>>> 	spin_lock_init(&buf->rb_lock);
>>> -	atomic_set(&buf->rb_credits, 1);
>>>
>>> 	/* Need to allocate:
>>> 	 *   1.  arrays for send and recv pointers
>>> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
>>> index 532d586..3fcc92b 100644
>>> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
>>> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
>>> @@ -248,7 +248,6 @@ struct rpcrdma_req {
>>>  */
>>> struct rpcrdma_buffer {
>>> 	spinlock_t	rb_lock;	/* protects indexes */
>>> -	atomic_t	rb_credits;	/* most recent server credits */
>>> 	int		rb_max_requests;/* client max requests */
>>> 	struct list_head rb_mws;	/* optional memory windows/fmrs/frmrs */
>>> 	struct list_head rb_all;
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>
> 
> --
> Chuck Lever
> chuck[dot]lever[at]oracle[dot]com
> 
> 
> 
> --
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> 

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Patch
diff mbox

diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
index dcf5ebc..d731010 100644
--- a/net/sunrpc/xprtrdma/rpc_rdma.c
+++ b/net/sunrpc/xprtrdma/rpc_rdma.c
@@ -736,7 +736,7 @@  rpcrdma_reply_handler(struct rpcrdma_rep *rep)
 	struct rpc_xprt *xprt = rep->rr_xprt;
 	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
 	__be32 *iptr;
-	int rdmalen, status;
+	int credits, rdmalen, status;
 	unsigned long cwnd;
 
 	/* Check status. If bad, signal disconnect and return rep to pool */
@@ -871,8 +871,14 @@  badheader:
 		break;
 	}
 
+	credits = be32_to_cpu(headerp->rm_credit);
+	if (credits == 0)
+		credits = 1;	/* don't deadlock */
+	else if (credits > r_xprt->rx_buf.rb_max_requests)
+		credits = r_xprt->rx_buf.rb_max_requests;
+
 	cwnd = xprt->cwnd;
-	xprt->cwnd = atomic_read(&r_xprt->rx_buf.rb_credits) << RPC_CWNDSHIFT;
+	xprt->cwnd = credits << RPC_CWNDSHIFT;
 	if (xprt->cwnd > cwnd)
 		xprt_release_rqst_cong(rqst->rq_task);
 
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 1000f63..71a071a 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -49,6 +49,7 @@ 
 
 #include <linux/interrupt.h>
 #include <linux/slab.h>
+#include <linux/prefetch.h>
 #include <asm/bitops.h>
 
 #include "xprt_rdma.h"
@@ -298,17 +299,7 @@  rpcrdma_recvcq_process_wc(struct ib_wc *wc, struct list_head *sched_list)
 	rep->rr_len = wc->byte_len;
 	ib_dma_sync_single_for_cpu(rdmab_to_ia(rep->rr_buffer)->ri_id->device,
 			rep->rr_iov.addr, rep->rr_len, DMA_FROM_DEVICE);
-
-	if (rep->rr_len >= 16) {
-		struct rpcrdma_msg *p = (struct rpcrdma_msg *)rep->rr_base;
-		unsigned int credits = ntohl(p->rm_credit);
-
-		if (credits == 0)
-			credits = 1;	/* don't deadlock */
-		else if (credits > rep->rr_buffer->rb_max_requests)
-			credits = rep->rr_buffer->rb_max_requests;
-		atomic_set(&rep->rr_buffer->rb_credits, credits);
-	}
+	prefetch(rep->rr_base);
 
 out_schedule:
 	list_add_tail(&rep->rr_list, sched_list);
@@ -480,7 +471,6 @@  rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
 	case RDMA_CM_EVENT_DEVICE_REMOVAL:
 		connstate = -ENODEV;
 connected:
-		atomic_set(&rpcx_to_rdmax(ep->rep_xprt)->rx_buf.rb_credits, 1);
 		dprintk("RPC:       %s: %sconnected\n",
 					__func__, connstate > 0 ? "" : "dis");
 		ep->rep_connected = connstate;
@@ -1186,7 +1176,6 @@  rpcrdma_buffer_create(struct rpcrdma_buffer *buf, struct rpcrdma_ep *ep,
 
 	buf->rb_max_requests = cdata->max_requests;
 	spin_lock_init(&buf->rb_lock);
-	atomic_set(&buf->rb_credits, 1);
 
 	/* Need to allocate:
 	 *   1.  arrays for send and recv pointers
diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
index 532d586..3fcc92b 100644
--- a/net/sunrpc/xprtrdma/xprt_rdma.h
+++ b/net/sunrpc/xprtrdma/xprt_rdma.h
@@ -248,7 +248,6 @@  struct rpcrdma_req {
  */
 struct rpcrdma_buffer {
 	spinlock_t	rb_lock;	/* protects indexes */
-	atomic_t	rb_credits;	/* most recent server credits */
 	int		rb_max_requests;/* client max requests */
 	struct list_head rb_mws;	/* optional memory windows/fmrs/frmrs */
 	struct list_head rb_all;