svcrdma: support Remote Invalidation

Support Remote Invalidation. A private message is exchanged with
the client upon RDMA transport connect that indicates whether
Send With Invalidation may be used by the server to send RPC
replies. The invalidate_rkey is arbitrarily chosen from among
rkeys present in the RPC-over-RDMA header's chunk lists.

Send With Invalidate improves performance only when clients can
recognize, while processing an RPC reply, that an rkey has already
been invalidated. That has been submitted as a separate change.

In the future, the RPC-over-RDMA protocol might support Remote
Invalidation properly. The protocol needs to enable signaling
between peers to indicate when Remote Invalidation can be used
for each individual RPC.

Signed-off-by: Chuck Lever <[e-mail]>
Reviewed-by: Sagi Grimberg <[e-mail]>
Signed-off-by: J. Bruce Fields <[e-mail]>

include/linux/sunrpc/svc_rdma.h

···
 	int		     sc_ord;		/* RDMA read limit */
 	int                  sc_max_sge;
 	int                  sc_max_sge_rd;	/* max sge for read target */
+	bool		     sc_snd_w_inv;	/* OK to use Send With Invalidate */
 
 	atomic_t             sc_sq_count;	/* Number of SQ WR on queue */
 	unsigned int	     sc_sq_depth;	/* Depth of SQ */

net/sunrpc/xprtrdma/svc_rdma_sendto.c

···
 	return rp_ary;
 }
 
+/* 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 rkey it finds in the chunks lists.
+ *
+ * Returns zero if RPC's chunk lists are empty.
+ */
+static u32 svc_rdma_get_inv_rkey(struct rpcrdma_msg *rdma_argp,
+				 struct rpcrdma_write_array *wr_ary,
+				 struct rpcrdma_write_array *rp_ary)
+{
+	struct rpcrdma_read_chunk *rd_ary;
+	struct rpcrdma_segment *arg_ch;
+	u32 inv_rkey;
+
+	inv_rkey = 0;
+
+	rd_ary = svc_rdma_get_read_chunk(rdma_argp);
+	if (rd_ary) {
+		inv_rkey = be32_to_cpu(rd_ary->rc_target.rs_handle);
+		goto out;
+	}
+
+	if (wr_ary && be32_to_cpu(wr_ary->wc_nchunks)) {
+		arg_ch = &wr_ary->wc_array[0].wc_target;
+		inv_rkey = be32_to_cpu(arg_ch->rs_handle);
+		goto out;
+	}
+
+	if (rp_ary && be32_to_cpu(rp_ary->wc_nchunks)) {
+		arg_ch = &rp_ary->wc_array[0].wc_target;
+		inv_rkey = be32_to_cpu(arg_ch->rs_handle);
+		goto out;
+	}
+
+out:
+	dprintk("svcrdma: Send With Invalidate rkey=%08x\n", inv_rkey);
+	return inv_rkey;
+}
+
 /* Assumptions:
  * - The specified write_len can be represented in sc_max_sge * PAGE_SIZE
  */
···
 		      struct page *page,
 		      struct rpcrdma_msg *rdma_resp,
 		      struct svc_rdma_req_map *vec,
-		      int byte_count)
+		      int byte_count,
+		      u32 inv_rkey)
 {
 	struct svc_rdma_op_ctxt *ctxt;
 	struct ib_send_wr send_wr;
···
 	send_wr.wr_cqe = &ctxt->cqe;
 	send_wr.sg_list = ctxt->sge;
 	send_wr.num_sge = sge_no;
-	send_wr.opcode = IB_WR_SEND;
+	if (inv_rkey) {
+		send_wr.opcode = IB_WR_SEND_WITH_INV;
+		send_wr.ex.invalidate_rkey = inv_rkey;
+	} else
+		send_wr.opcode = IB_WR_SEND;
 	send_wr.send_flags =  IB_SEND_SIGNALED;
 
 	ret = svc_rdma_send(rdma, &send_wr);
···
 	int inline_bytes;
 	struct page *res_page;
 	struct svc_rdma_req_map *vec;
+	u32 inv_rkey;
 
 	dprintk("svcrdma: sending response for rqstp=%p\n", rqstp);
 
···
 	rdma_argp = page_address(rqstp->rq_pages[0]);
 	wr_ary = svc_rdma_get_write_array(rdma_argp);
 	rp_ary = svc_rdma_get_reply_array(rdma_argp, wr_ary);
+
+	inv_rkey = 0;
+	if (rdma->sc_snd_w_inv)
+		inv_rkey = svc_rdma_get_inv_rkey(rdma_argp, wr_ary, rp_ary);
 
 	/* Build an req vec for the XDR */
 	vec = svc_rdma_get_req_map(rdma);
···
 		goto err1;
 
 	ret = send_reply(rdma, rqstp, res_page, rdma_resp, vec,
-			 inline_bytes);
+			 inline_bytes, inv_rkey);
 	if (ret < 0)
 		goto err0;
 

net/sunrpc/xprtrdma/svc_rdma_transport.c

···
 	if (pmsg &&
 	    pmsg->cp_magic == rpcrdma_cmp_magic &&
 	    pmsg->cp_version == RPCRDMA_CMP_VERSION) {
-		dprintk("svcrdma: client send_size %u, recv_size %u\n",
+		newxprt->sc_snd_w_inv = pmsg->cp_flags &
+					RPCRDMA_CMP_F_SND_W_INV_OK;
+
+		dprintk("svcrdma: client send_size %u, recv_size %u "
+			"remote inv %ssupported\n",
 			rpcrdma_decode_buffer_size(pmsg->cp_send_size),
-			rpcrdma_decode_buffer_size(pmsg->cp_recv_size));
+			rpcrdma_decode_buffer_size(pmsg->cp_recv_size),
+			newxprt->sc_snd_w_inv ? "" : "un");
 	}
 }
 
···
 			dev->attrs.max_fast_reg_page_list_len;
 		newxprt->sc_dev_caps |= SVCRDMA_DEVCAP_FAST_REG;
 		newxprt->sc_reader = rdma_read_chunk_frmr;
-	}
+	} else
+		newxprt->sc_snd_w_inv = false;
 
 	/*
 	 * Determine if a DMA MR is required and if so, what privs are required