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Commit eba8ff66 authored by Chuck Lever's avatar Chuck Lever Committed by Anna Schumaker
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xprtrdma: Move credit update to RPC reply handler 



Reduce work in the receive CQ handler, which can be 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 (the CPU stalls while
waiting for the header contents to be brought into the cache).

This further extends work begun by commit e7ce710a ("xprtrdma:
Avoid deadlock when credit window is reset").

Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
Reviewed-by: default avatarSteve Wise <swise@opengridcomputing.com>
Signed-off-by: default avatarAnna Schumaker <Anna.Schumaker@Netapp.com>
parent 3eb35810

net/sunrpc/xprtrdma/rpc_rdma.c

+8 −2
Original line number Diff line number Diff line
@@ -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 @@ rpcrdma_reply_handler(struct rpcrdma_rep *rep) 
		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);

net/sunrpc/xprtrdma/verbs.c

+2 −13
Original line number Diff line number Diff line
@@ -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

net/sunrpc/xprtrdma/xprt_rdma.h

+0 −1
Original line number Diff line number Diff line
@@ -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;