[PATCH v3 12/21] xprtrdma: Clean up sendctx functions

[Chuck Lever <chuck.lever@oracle.com>]

Minor clean-ups I've stumbled on since sendctx was merged last year.
In particular, making Send completion processing more efficient
appears to have a measurable impact on IOPS throughput.

Note: test_and_clear_bit() returns a value, thus an explicit memory
barrier is not necessary.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/xprtrdma/rpc_rdma.c  |   27 ++++++++++++---------------
 net/sunrpc/xprtrdma/verbs.c     |   17 ++++++++---------
 net/sunrpc/xprtrdma/xprt_rdma.h |    5 +++--
 3 files changed, 23 insertions(+), 26 deletions(-)

diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
index 45cba06..5cb060c 100644
--- a/net/sunrpc/xprtrdma/rpc_rdma.c
+++ b/net/sunrpc/xprtrdma/rpc_rdma.c
@@ -508,30 +508,26 @@ static bool rpcrdma_results_inline(struct rpcrdma_xprt *r_xprt,
 }
 
 /**
- * rpcrdma_unmap_sendctx - DMA-unmap Send buffers
+ * rpcrdma_sendctx_unmap - DMA-unmap Send buffer
  * @sc: sendctx containing SGEs to unmap
  *
  */
-void
-rpcrdma_unmap_sendctx(struct rpcrdma_sendctx *sc)
+void rpcrdma_sendctx_unmap(struct rpcrdma_sendctx *sc)
 {
-	struct rpcrdma_ia *ia = &sc->sc_xprt->rx_ia;
 	struct ib_sge *sge;
-	unsigned int count;
 
 	/* The first two SGEs contain the transport header and
 	 * the inline buffer. These are always left mapped so
 	 * they can be cheaply re-used.
 	 */
-	sge = &sc->sc_sges[2];
-	for (count = sc->sc_unmap_count; count; ++sge, --count)
-		ib_dma_unmap_page(ia->ri_device,
-				  sge->addr, sge->length, DMA_TO_DEVICE);
+	for (sge = &sc->sc_sges[2]; sc->sc_unmap_count;
+	     ++sge, --sc->sc_unmap_count)
+		ib_dma_unmap_page(sc->sc_device, sge->addr, sge->length,
+				  DMA_TO_DEVICE);
 
-	if (test_and_clear_bit(RPCRDMA_REQ_F_TX_RESOURCES, &sc->sc_req->rl_flags)) {
-		smp_mb__after_atomic();
+	if (test_and_clear_bit(RPCRDMA_REQ_F_TX_RESOURCES,
+			       &sc->sc_req->rl_flags))
 		wake_up_bit(&sc->sc_req->rl_flags, RPCRDMA_REQ_F_TX_RESOURCES);
-	}
 }
 
 /* Prepare an SGE for the RPC-over-RDMA transport header.
@@ -578,6 +574,7 @@ static bool rpcrdma_prepare_msg_sges(struct rpcrdma_xprt *r_xprt,
 	 */
 	if (!rpcrdma_regbuf_dma_map(r_xprt, rb))
 		goto out_regbuf;
+	sc->sc_device = rdmab_device(rb);
 	sge_no = 1;
 	sge[sge_no].addr = rdmab_addr(rb);
 	sge[sge_no].length = xdr->head[0].iov_len;
@@ -673,12 +670,12 @@ static bool rpcrdma_prepare_msg_sges(struct rpcrdma_xprt *r_xprt,
 	return false;
 
 out_mapping_overflow:
-	rpcrdma_unmap_sendctx(sc);
+	rpcrdma_sendctx_unmap(sc);
 	pr_err("rpcrdma: too many Send SGEs (%u)\n", sge_no);
 	return false;
 
 out_mapping_err:
-	rpcrdma_unmap_sendctx(sc);
+	rpcrdma_sendctx_unmap(sc);
 	trace_xprtrdma_dma_maperr(sge[sge_no].addr);
 	return false;
 }
@@ -698,7 +695,7 @@ static bool rpcrdma_prepare_msg_sges(struct rpcrdma_xprt *r_xprt,
 			  struct rpcrdma_req *req, u32 hdrlen,
 			  struct xdr_buf *xdr, enum rpcrdma_chunktype rtype)
 {
-	req->rl_sendctx = rpcrdma_sendctx_get_locked(&r_xprt->rx_buf);
+	req->rl_sendctx = rpcrdma_sendctx_get_locked(r_xprt);
 	if (!req->rl_sendctx)
 		return -EAGAIN;
 	req->rl_sendctx->sc_wr.num_sge = 0;
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 81548fc2..1ad2519 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -870,20 +870,20 @@ static unsigned long rpcrdma_sendctx_next(struct rpcrdma_buffer *buf,
 
 /**
  * rpcrdma_sendctx_get_locked - Acquire a send context
- * @buf: transport buffers from which to acquire an unused context
+ * @r_xprt: controlling transport instance
  *
  * Returns pointer to a free send completion context; or NULL if
  * the queue is empty.
  *
  * Usage: Called to acquire an SGE array before preparing a Send WR.
  *
- * The caller serializes calls to this function (per rpcrdma_buffer),
- * and provides an effective memory barrier that flushes the new value
+ * The caller serializes calls to this function (per transport), and
+ * provides an effective memory barrier that flushes the new value
  * of rb_sc_head.
  */
-struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_buffer *buf)
+struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_xprt *r_xprt)
 {
-	struct rpcrdma_xprt *r_xprt;
+	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
 	struct rpcrdma_sendctx *sc;
 	unsigned long next_head;
 
@@ -908,7 +908,6 @@ struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_buffer *buf)
 	 * backing up. Cause the caller to pause and try again.
 	 */
 	set_bit(RPCRDMA_BUF_F_EMPTY_SCQ, &buf->rb_flags);
-	r_xprt = container_of(buf, struct rpcrdma_xprt, rx_buf);
 	r_xprt->rx_stats.empty_sendctx_q++;
 	return NULL;
 }
@@ -920,7 +919,7 @@ struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_buffer *buf)
  * Usage: Called from Send completion to return a sendctxt
  * to the queue.
  *
- * The caller serializes calls to this function (per rpcrdma_buffer).
+ * The caller serializes calls to this function (per transport).
  */
 static void
 rpcrdma_sendctx_put_locked(struct rpcrdma_sendctx *sc)
@@ -928,7 +927,7 @@ struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_buffer *buf)
 	struct rpcrdma_buffer *buf = &sc->sc_xprt->rx_buf;
 	unsigned long next_tail;
 
-	/* Unmap SGEs of previously completed by unsignaled
+	/* Unmap SGEs of previously completed but unsignaled
 	 * Sends by walking up the queue until @sc is found.
 	 */
 	next_tail = buf->rb_sc_tail;
@@ -936,7 +935,7 @@ struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_buffer *buf)
 		next_tail = rpcrdma_sendctx_next(buf, next_tail);
 
 		/* ORDER: item must be accessed _before_ tail is updated */
-		rpcrdma_unmap_sendctx(buf->rb_sc_ctxs[next_tail]);
+		rpcrdma_sendctx_unmap(buf->rb_sc_ctxs[next_tail]);
 
 	} while (buf->rb_sc_ctxs[next_tail] != sc);
 
diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
index 7621e2d..8afb5fc 100644
--- a/net/sunrpc/xprtrdma/xprt_rdma.h
+++ b/net/sunrpc/xprtrdma/xprt_rdma.h
@@ -225,6 +225,7 @@ enum {
 struct rpcrdma_sendctx {
 	struct ib_send_wr	sc_wr;
 	struct ib_cqe		sc_cqe;
+	struct ib_device	*sc_device;
 	struct rpcrdma_xprt	*sc_xprt;
 	struct rpcrdma_req	*sc_req;
 	unsigned int		sc_unmap_count;
@@ -536,7 +537,7 @@ struct rpcrdma_req *rpcrdma_req_create(struct rpcrdma_xprt *r_xprt, size_t size,
 void rpcrdma_req_destroy(struct rpcrdma_req *req);
 int rpcrdma_buffer_create(struct rpcrdma_xprt *);
 void rpcrdma_buffer_destroy(struct rpcrdma_buffer *);
-struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_buffer *buf);
+struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_xprt *r_xprt);
 
 struct rpcrdma_mr *rpcrdma_mr_get(struct rpcrdma_xprt *r_xprt);
 void rpcrdma_mr_put(struct rpcrdma_mr *mr);
@@ -625,7 +626,7 @@ int rpcrdma_prepare_send_sges(struct rpcrdma_xprt *r_xprt,
 			      struct rpcrdma_req *req, u32 hdrlen,
 			      struct xdr_buf *xdr,
 			      enum rpcrdma_chunktype rtype);
-void rpcrdma_unmap_sendctx(struct rpcrdma_sendctx *sc);
+void rpcrdma_sendctx_unmap(struct rpcrdma_sendctx *sc);
 int rpcrdma_marshal_req(struct rpcrdma_xprt *r_xprt, struct rpc_rqst *rqst);
 void rpcrdma_set_max_header_sizes(struct rpcrdma_xprt *);
 void rpcrdma_complete_rqst(struct rpcrdma_rep *rep);