[RFC,2/2] xprtrdma: Reduce the doorbell rate (Receive)

Commit Message

Chuck Lever Jan. 16, 2019, 6:22 p.m. UTC

Post RECV WRs in batches to reduce the hardware doorbell rate per
transport. This helps the RPC-over-RDMA client scale better in
number of transports.

Signed-off-by: Chuck Lever <[e-mail]>
---
 net/sunrpc/xprtrdma/verbs.c     |    2 ++
 net/sunrpc/xprtrdma/xprt_rdma.h |   11 +++++++++++
 2 files changed, 13 insertions(+)

Patch

diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 7749a2b..0d3ec6f 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -1482,6 +1482,8 @@  struct rpcrdma_regbuf *
 	if (ep->rep_receive_count > needed)
 		goto out;
 	needed -= ep->rep_receive_count;
+	if (!temp)
+		needed += RPCRDMA_MAX_RECV_BATCH;
 
 	count = 0;
 	wr = NULL;
diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
index 5a18472..47ded5c 100644
--- a/net/sunrpc/xprtrdma/xprt_rdma.h
+++ b/net/sunrpc/xprtrdma/xprt_rdma.h
@@ -205,6 +205,17 @@  struct rpcrdma_rep {
 	struct ib_recv_wr	rr_recv_wr;
 };
 
+/* To reduce the rate at which a transport invokes ib_post_recv
+ * (and thus the hardware doorbell rate), xprtrdma posts Receive
+ * WRs in batches.
+ *
+ * Setting this to zero disables Receive post batching.
+ */
+enum {
+	RPCRDMA_MAX_RECV_BATCH = 7,
+};
+
+
 /* struct rpcrdma_sendctx - DMA mapped SGEs to unmap after Send completes
  */
 struct rpcrdma_req;