svcrdma: Allocate recv_ctxt's on CPU handling Receives

There is a significant latency penalty when processing an ingress
Receive if the Receive buffer resides in memory that is not on the
same NUMA node as the the CPU handling completions for a CQ.

The system administrator and the device driver determine which CPU
handles completions. This CPU does not change during life of the CQ.
Further the Upper Layer does not have any visibility of which CPU it
is.

Allocating Receive buffers in the Receive completion handler
guarantees that Receive buffers are allocated on the preferred NUMA
node for that CQ.

Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: J. Bruce Fields <[email protected]>

include/linux/sunrpc/svc_rdma.h

@@ -151,6 +151,7 @@ struct svc_rdma_recv_ctxt {
 	struct ib_sge		rc_recv_sge;
 	void			*rc_recv_buf;
 	struct xdr_buf		rc_arg;
+	bool			rc_temp;
 	u32			rc_byte_len;
 	unsigned int		rc_page_count;
 	unsigned int		rc_hdr_count;

net/sunrpc/xprtrdma/svc_rdma_recvfrom.c

@@ -144,6 +144,7 @@ svc_rdma_recv_ctxt_alloc(struct svcxprt_rdma *rdma)
 	ctxt->rc_recv_sge.length = rdma->sc_max_req_size;
 	ctxt->rc_recv_sge.lkey = rdma->sc_pd->local_dma_lkey;
 	ctxt->rc_recv_buf = buffer;
+	ctxt->rc_temp = false;
 	return ctxt;
 
 fail2:
@@ -154,6 +155,15 @@ svc_rdma_recv_ctxt_alloc(struct svcxprt_rdma *rdma)
 	return NULL;
 }
 
+static void svc_rdma_recv_ctxt_destroy(struct svcxprt_rdma *rdma,
+				       struct svc_rdma_recv_ctxt *ctxt)
+{
+	ib_dma_unmap_single(rdma->sc_pd->device, ctxt->rc_recv_sge.addr,
+			    ctxt->rc_recv_sge.length, DMA_FROM_DEVICE);
+	kfree(ctxt->rc_recv_buf);
+	kfree(ctxt);
+}
+
 /**
  * svc_rdma_recv_ctxts_destroy - Release all recv_ctxt's for an xprt
  * @rdma: svcxprt_rdma being torn down
@@ -165,12 +175,7 @@ void svc_rdma_recv_ctxts_destroy(struct svcxprt_rdma *rdma)
 
 	while ((ctxt = svc_rdma_next_recv_ctxt(&rdma->sc_recv_ctxts))) {
 		list_del(&ctxt->rc_list);
-		ib_dma_unmap_single(rdma->sc_pd->device,
-				    ctxt->rc_recv_sge.addr,
-				    ctxt->rc_recv_sge.length,
-				    DMA_FROM_DEVICE);
-		kfree(ctxt->rc_recv_buf);
-		kfree(ctxt);
+		svc_rdma_recv_ctxt_destroy(rdma, ctxt);
 	}
 }
 
@@ -212,21 +217,21 @@ void svc_rdma_recv_ctxt_put(struct svcxprt_rdma *rdma,
 
 	for (i = 0; i < ctxt->rc_page_count; i++)
 		put_page(ctxt->rc_pages[i]);
-	spin_lock(&rdma->sc_recv_lock);
-	list_add(&ctxt->rc_list, &rdma->sc_recv_ctxts);
-	spin_unlock(&rdma->sc_recv_lock);
+
+	if (!ctxt->rc_temp) {
+		spin_lock(&rdma->sc_recv_lock);
+		list_add(&ctxt->rc_list, &rdma->sc_recv_ctxts);
+		spin_unlock(&rdma->sc_recv_lock);
+	} else
+		svc_rdma_recv_ctxt_destroy(rdma, ctxt);
 }
 
-static int svc_rdma_post_recv(struct svcxprt_rdma *rdma)
+static int __svc_rdma_post_recv(struct svcxprt_rdma *rdma,
+				struct svc_rdma_recv_ctxt *ctxt)
 {
-	struct svc_rdma_recv_ctxt *ctxt;
 	struct ib_recv_wr *bad_recv_wr;
 	int ret;
 
-	ctxt = svc_rdma_recv_ctxt_get(rdma);
-	if (!ctxt)
-		return -ENOMEM;
-
 	svc_xprt_get(&rdma->sc_xprt);
 	ret = ib_post_recv(rdma->sc_qp, &ctxt->rc_recv_wr, &bad_recv_wr);
 	trace_svcrdma_post_recv(&ctxt->rc_recv_wr, ret);
@@ -240,6 +245,16 @@ static int svc_rdma_post_recv(struct svcxprt_rdma *rdma)
 	return ret;
 }
 
+static int svc_rdma_post_recv(struct svcxprt_rdma *rdma)
+{
+	struct svc_rdma_recv_ctxt *ctxt;
+
+	ctxt = svc_rdma_recv_ctxt_get(rdma);
+	if (!ctxt)
+		return -ENOMEM;
+	return __svc_rdma_post_recv(rdma, ctxt);
+}
+
 /**
  * svc_rdma_post_recvs - Post initial set of Recv WRs
  * @rdma: fresh svcxprt_rdma
@@ -248,11 +263,16 @@ static int svc_rdma_post_recv(struct svcxprt_rdma *rdma)
  */
 bool svc_rdma_post_recvs(struct svcxprt_rdma *rdma)
 {
+	struct svc_rdma_recv_ctxt *ctxt;
 	unsigned int i;
 	int ret;
 
 	for (i = 0; i < rdma->sc_max_requests; i++) {
-		ret = svc_rdma_post_recv(rdma);
+		ctxt = svc_rdma_recv_ctxt_get(rdma);
+		if (!ctxt)
+			return -ENOMEM;
+		ctxt->rc_temp = true;
+		ret = __svc_rdma_post_recv(rdma, ctxt);
 		if (ret) {
 			pr_err("svcrdma: failure posting recv buffers: %d\n",
 			       ret);