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Subject: [PATCH v1] svcrdma: Optimize the logic that selects the R_key to
 invalidate
From:   Chuck Lever <chuck.lever@oracle.com>
To:     linux-rdma@vger.kernel.org, linux-nfs@vger.kernel.org
Date:   Tue, 27 Nov 2018 11:11:35 -0500
Message-ID: <20181127161016.6997.69002.stgit@klimt.1015granger.net>
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o Select the R_key to invalidate while the CPU cache still contains
  the received RPC Call transport header, rather than waiting until
  we're about to send the RPC Reply.

o Choose Send With Invalidate if there is exactly one distinct R_key
  in the received transport header. If there's more than one, the
  client will have to perform local invalidation after it has
  already waited for remote invalidation.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
Hi-

Please consider this NFS server-side patch for v4.21.


 include/linux/sunrpc/svc_rdma.h         |    1 
 net/sunrpc/xprtrdma/svc_rdma_recvfrom.c |   63 +++++++++++++++++++++++++++++++
 net/sunrpc/xprtrdma/svc_rdma_sendto.c   |   53 ++++++--------------------
 3 files changed, 77 insertions(+), 40 deletions(-)

diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
index e6e2691..7e22681 100644
--- a/include/linux/sunrpc/svc_rdma.h
+++ b/include/linux/sunrpc/svc_rdma.h
@@ -135,6 +135,7 @@ struct svc_rdma_recv_ctxt {
 	u32			rc_byte_len;
 	unsigned int		rc_page_count;
 	unsigned int		rc_hdr_count;
+	u32			rc_inv_rkey;
 	struct page		*rc_pages[RPCSVC_MAXPAGES];
 };
 
diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
index b24d5b8..828b149 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
@@ -485,6 +485,68 @@ static __be32 *xdr_check_reply_chunk(__be32 *p, const __be32 *end)
 	return p;
 }
 
+/* RPC-over-RDMA Version One private extension: Remote Invalidation.
+ * Responder's choice: requester signals it can handle Send With
+ * Invalidate, and responder chooses one R_key to invalidate.
+ *
+ * If there is exactly one distinct R_key in the received transport
+ * header, set rc_inv_rkey to that R_key. Otherwise, set it to zero.
+ *
+ * Perform this operation while the received transport header is
+ * still in the CPU cache.
+ */
+static void svc_rdma_get_inv_rkey(struct svcxprt_rdma *rdma,
+				  struct svc_rdma_recv_ctxt *ctxt)
+{
+	__be32 inv_rkey, *p;
+	u32 i, segcount;
+
+	ctxt->rc_inv_rkey = 0;
+
+	if (!rdma->sc_snd_w_inv)
+		return;
+
+	inv_rkey = xdr_zero;
+	p = ctxt->rc_recv_buf;
+	p += rpcrdma_fixed_maxsz;
+
+	/* Read list */
+	while (*p++ != xdr_zero) {
+		p++;	/* position */
+		if (inv_rkey == xdr_zero)
+			inv_rkey = *p;
+		else if (inv_rkey != *p)
+			return;
+		p += 4;
+	}
+
+	/* Write list */
+	while (*p++ != xdr_zero) {
+		segcount = be32_to_cpup(p++);
+		for (i = 0; i < segcount; i++) {
+			if (inv_rkey == xdr_zero)
+				inv_rkey = *p;
+			else if (inv_rkey != *p)
+				return;
+			p += 4;
+		}
+	}
+
+	/* Reply chunk */
+	if (*p++ != xdr_zero) {
+		segcount = be32_to_cpup(p++);
+		for (i = 0; i < segcount; i++) {
+			if (inv_rkey == xdr_zero)
+				inv_rkey = *p;
+			else if (inv_rkey != *p)
+				return;
+			p += 4;
+		}
+	}
+
+	ctxt->rc_inv_rkey = be32_to_cpu(inv_rkey);
+}
+
 /* On entry, xdr->head[0].iov_base points to first byte in the
  * RPC-over-RDMA header.
  *
@@ -746,6 +808,7 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
 		svc_rdma_recv_ctxt_put(rdma_xprt, ctxt);
 		return ret;
 	}
+	svc_rdma_get_inv_rkey(rdma_xprt, ctxt);
 
 	p += rpcrdma_fixed_maxsz;
 	if (*p != xdr_zero)
diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
index 8602a5f..d48bc6d 100644
--- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
@@ -484,32 +484,6 @@ static void svc_rdma_get_write_arrays(__be32 *rdma_argp,
 		*reply = NULL;
 }
 
-/* RPC-over-RDMA Version One private extension: Remote Invalidation.
- * Responder's choice: requester signals it can handle Send With
- * Invalidate, and responder chooses one rkey to invalidate.
- *
- * Find a candidate rkey to invalidate when sending a reply.  Picks the
- * first R_key it finds in the chunk lists.
- *
- * Returns zero if RPC's chunk lists are empty.
- */
-static u32 svc_rdma_get_inv_rkey(__be32 *rdma_argp,
-				 __be32 *wr_lst, __be32 *rp_ch)
-{
-	__be32 *p;
-
-	p = rdma_argp + rpcrdma_fixed_maxsz;
-	if (*p != xdr_zero)
-		p += 2;
-	else if (wr_lst && be32_to_cpup(wr_lst + 1))
-		p = wr_lst + 2;
-	else if (rp_ch && be32_to_cpup(rp_ch + 1))
-		p = rp_ch + 2;
-	else
-		return 0;
-	return be32_to_cpup(p);
-}
-
 static int svc_rdma_dma_map_page(struct svcxprt_rdma *rdma,
 				 struct svc_rdma_send_ctxt *ctxt,
 				 struct page *page,
@@ -672,7 +646,7 @@ static void svc_rdma_save_io_pages(struct svc_rqst *rqstp,
  *
  * RDMA Send is the last step of transmitting an RPC reply. Pages
  * involved in the earlier RDMA Writes are here transferred out
- * of the rqstp and into the ctxt's page array. These pages are
+ * of the rqstp and into the sctxt's page array. These pages are
  * DMA unmapped by each Write completion, but the subsequent Send
  * completion finally releases these pages.
  *
@@ -680,32 +654,31 @@ static void svc_rdma_save_io_pages(struct svc_rqst *rqstp,
  * - The Reply's transport header will never be larger than a page.
  */
 static int svc_rdma_send_reply_msg(struct svcxprt_rdma *rdma,
-				   struct svc_rdma_send_ctxt *ctxt,
-				   __be32 *rdma_argp,
+				   struct svc_rdma_send_ctxt *sctxt,
+				   struct svc_rdma_recv_ctxt *rctxt,
 				   struct svc_rqst *rqstp,
 				   __be32 *wr_lst, __be32 *rp_ch)
 {
 	int ret;
 
 	if (!rp_ch) {
-		ret = svc_rdma_map_reply_msg(rdma, ctxt,
+		ret = svc_rdma_map_reply_msg(rdma, sctxt,
 					     &rqstp->rq_res, wr_lst);
 		if (ret < 0)
 			return ret;
 	}
 
-	svc_rdma_save_io_pages(rqstp, ctxt);
+	svc_rdma_save_io_pages(rqstp, sctxt);
 
-	ctxt->sc_send_wr.opcode = IB_WR_SEND;
-	if (rdma->sc_snd_w_inv) {
-		ctxt->sc_send_wr.ex.invalidate_rkey =
-			svc_rdma_get_inv_rkey(rdma_argp, wr_lst, rp_ch);
-		if (ctxt->sc_send_wr.ex.invalidate_rkey)
-			ctxt->sc_send_wr.opcode = IB_WR_SEND_WITH_INV;
+	if (rctxt->rc_inv_rkey) {
+		sctxt->sc_send_wr.opcode = IB_WR_SEND_WITH_INV;
+		sctxt->sc_send_wr.ex.invalidate_rkey = rctxt->rc_inv_rkey;
+	} else {
+		sctxt->sc_send_wr.opcode = IB_WR_SEND;
 	}
 	dprintk("svcrdma: posting Send WR with %u sge(s)\n",
-		ctxt->sc_send_wr.num_sge);
-	return svc_rdma_send(rdma, &ctxt->sc_send_wr);
+		sctxt->sc_send_wr.num_sge);
+	return svc_rdma_send(rdma, &sctxt->sc_send_wr);
 }
 
 /* Given the client-provided Write and Reply chunks, the server was not
@@ -809,7 +782,7 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
 	}
 
 	svc_rdma_sync_reply_hdr(rdma, sctxt, svc_rdma_reply_hdr_len(rdma_resp));
-	ret = svc_rdma_send_reply_msg(rdma, sctxt, rdma_argp, rqstp,
+	ret = svc_rdma_send_reply_msg(rdma, sctxt, rctxt, rqstp,
 				      wr_lst, rp_ch);
 	if (ret < 0)
 		goto err1;