svcrdma: Don't account for Receive queue "starvation"

>From what I can tell, calling ->recvfrom when there is no work to do
is a normal part of operation. This is the only way svc_recv can
tell when there is no more data ready to receive on the transport.

Neither the TCP nor the UDP transport implementations have a
"starve" metric.

The cost of receive starvation accounting is bumping an atomic, which
results in extra (IMO unnecessary) bus traffic between CPU sockets,
while holding a spin lock.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 6 insertions, 15 deletions

diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
index b48089314f85..1452bd02d857 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -844,9 +844,9 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
         struct svc_xprt *xprt = rqstp->rq_xprt;
         struct svcxprt_rdma *rdma_xprt =
                 container_of(xprt, struct svcxprt_rdma, sc_xprt);
-        struct svc_rdma_op_ctxt *ctxt = NULL;
+        struct svc_rdma_op_ctxt *ctxt;
         struct rpcrdma_msg *rmsgp;
-        int ret = 0;
+        int ret;
 
         dprintk("svcrdma: rqstp=%p\n", rqstp);
 
@@ -863,21 +863,13 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
                                         struct svc_rdma_op_ctxt, list);
                 list_del(&ctxt->list);
         } else {
-                atomic_inc(&rdma_stat_rq_starve);
+                /* No new incoming requests, terminate the loop */
                 clear_bit(XPT_DATA, &xprt->xpt_flags);
-                ctxt = NULL;
+                spin_unlock(&rdma_xprt->sc_rq_dto_lock);
+                return 0;
         }
         spin_unlock(&rdma_xprt->sc_rq_dto_lock);
-        if (!ctxt) {
-                /* This is the EAGAIN path. The svc_recv routine will
-                 * return -EAGAIN, the nfsd thread will go to call into
-                 * svc_recv again and we shouldn't be on the active
-                 * transport list
-                 */
-                if (test_bit(XPT_CLOSE, &xprt->xpt_flags))
-                        goto defer;
-                goto out;
-        }
+
         dprintk("svcrdma: processing ctxt=%p on xprt=%p, rqstp=%p\n",
                 ctxt, rdma_xprt, rqstp);
         atomic_inc(&rdma_stat_recv);
@@ -920,7 +912,6 @@ complete:
                 + rqstp->rq_arg.page_len
                 + rqstp->rq_arg.tail[0].iov_len;
         svc_rdma_put_context(ctxt, 0);
- out:
         dprintk("svcrdma: ret=%d, rq_arg.len=%u, "
                 "rq_arg.head[0].iov_base=%p, rq_arg.head[0].iov_len=%zd\n",
                 ret, rqstp->rq_arg.len,