xprtrdma: Limit work done by completion handler

Sagi Grimberg <sagig@dev.mellanox.co.il> points out that a steady
stream of CQ events could starve other work because of the boundless
loop pooling in rpcrdma_{send,recv}_poll().

Instead of a (potentially infinite) while loop, return after
collecting a budgeted number of completions.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Acked-by: Sagi Grimberg <sagig@dev.mellanox.co.il>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

2 files changed, 7 insertions, 4 deletions

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index b8caee91661c..1d083664bfca 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -165,8 +165,9 @@ static int
 rpcrdma_sendcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
 {
         struct ib_wc *wcs;
-        int count, rc;
+        int budget, count, rc;
 
+        budget = RPCRDMA_WC_BUDGET / RPCRDMA_POLLSIZE;
         do {
                 wcs = ep->rep_send_wcs;
 
@@ -177,7 +178,7 @@ rpcrdma_sendcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
                 count = rc;
                 while (count-- > 0)
                         rpcrdma_sendcq_process_wc(wcs++);
-        } while (rc == RPCRDMA_POLLSIZE);
+        } while (rc == RPCRDMA_POLLSIZE && --budget);
         return 0;
 }
 
@@ -254,8 +255,9 @@ static int
 rpcrdma_recvcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
 {
         struct ib_wc *wcs;
-        int count, rc;
+        int budget, count, rc;
 
+        budget = RPCRDMA_WC_BUDGET / RPCRDMA_POLLSIZE;
         do {
                 wcs = ep->rep_recv_wcs;
 
@@ -266,7 +268,7 @@ rpcrdma_recvcq_poll(struct ib_cq *cq, struct rpcrdma_ep *ep)
                 count = rc;
                 while (count-- > 0)
                         rpcrdma_recvcq_process_wc(wcs++);
-        } while (rc == RPCRDMA_POLLSIZE);
+        } while (rc == RPCRDMA_POLLSIZE && --budget);
         return 0;
 }
 
diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
index cb4c882b97fe..0c3b88ea5edb 100644
--- a/net/sunrpc/xprtrdma/xprt_rdma.h
+++ b/net/sunrpc/xprtrdma/xprt_rdma.h
@@ -74,6 +74,7 @@ struct rpcrdma_ia {
  * RDMA Endpoint -- one per transport instance
  */
 
+#define RPCRDMA_WC_BUDGET       (128)
 #define RPCRDMA_POLLSIZE        (16)
 
 struct rpcrdma_ep {