Re: [PATCH v12 08/26] nvme-tcp: Add DDP data-path

From: Boris Pismenny <borisp@nvidia.com>

Introduce the NVMe-TCP DDP data-path offload.
Using this interface, the NIC hardware will scatter TCP payload directly
to the BIO pages according to the command_id in the PDU.
To maintain the correctness of the network stack, the driver is expected
to construct SKBs that point to the BIO pages.

The data-path interface contains two routines: setup/teardown.
The setup provides the mapping from command_id to the request buffers,
while the teardown removes this mapping.

For efficiency, we introduce an asynchronous nvme completion, which is
split between NVMe-TCP and the NIC driver as follows:
NVMe-TCP performs the specific completion, while NIC driver performs the
generic mq_blk completion.

Signed-off-by: Boris Pismenny <borisp@nvidia.com>
Signed-off-by: Ben Ben-Ishay <redacted>
Signed-off-by: Or Gerlitz <redacted>
Signed-off-by: Yoray Zack <redacted>
Signed-off-by: Shai Malin <redacted>
Signed-off-by: Aurelien Aptel <redacted>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
---
  drivers/nvme/host/tcp.c | 121 ++++++++++++++++++++++++++++++++++++++--
  1 file changed, 116 insertions(+), 5 deletions(-)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 7d3b0ac65c03..6057cd424a19 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c

@@ -116,6 +116,13 @@ struct nvme_tcp_request {
  	size_t			offset;
  	size_t			data_sent;
  	enum nvme_tcp_send_state state;
+
+#ifdef CONFIG_ULP_DDP
+	bool			offloaded;
+	struct ulp_ddp_io	ddp;
+	__le16			ddp_status;
+	union nvme_result	result;
+#endif
  };
  
  enum nvme_tcp_queue_flags {

@@ -354,11 +361,75 @@ static inline bool is_netdev_ulp_offload_active(struct net_device *netdev,
  	return false;
  }
  
+static int nvme_tcp_req_map_ddp_sg(struct nvme_tcp_request *req, struct request *rq)

+	if (ret)
+		return -ENOMEM;
+
+	ret = netdev->netdev_ops->ulp_ddp_ops->setup(netdev, queue->sock->sk,
+						     &req->ddp);
+	if (ret) {
+		sg_free_table_chained(&req->ddp.sg_table, SG_CHUNK_SIZE);
+		return ret;
+	}
+
+	/* if successful, sg table is freed in nvme_tcp_teardown_ddp() */
+	req->offloaded = true;
+	return 0;
+}
+
  static int nvme_tcp_offload_socket(struct nvme_tcp_queue *queue)
  {
  	struct net_device *netdev = queue->ctrl->offloading_netdev;

@@ -491,6 +562,12 @@ static inline bool is_netdev_ulp_offload_active(struct net_device *netdev,
  	return false;
  }
  
+static int nvme_tcp_setup_ddp(struct nvme_tcp_queue *queue, u16 command_id,
+			      struct request *rq)
+{
+	return 0;
+}
+
  static int nvme_tcp_offload_socket(struct nvme_tcp_queue *queue)
  {
  	return -EOPNOTSUPP;

@@ -778,6 +855,26 @@ static void nvme_tcp_error_recovery(struct nvme_ctrl *ctrl)
  	queue_work(nvme_reset_wq, &to_tcp_ctrl(ctrl)->err_work);
  }
  
+static void nvme_tcp_complete_request(struct request *rq,
+				      __le16 status,
+				      union nvme_result result,
+				      __u16 command_id)
+{
+#ifdef CONFIG_ULP_DDP
+	struct nvme_tcp_request *req = blk_mq_rq_to_pdu(rq);
+
+	if (req->offloaded) {
+		req->ddp_status = status;
+		req->result = result;
+		nvme_tcp_teardown_ddp(req->queue, rq);
+		return;
+	}
+#endif
+
+	if (!nvme_try_complete_req(rq, status, result))
+		nvme_complete_rq(rq);
+}
+
  static int nvme_tcp_process_nvme_cqe(struct nvme_tcp_queue *queue,
  		struct nvme_completion *cqe)
  {

@@ -797,10 +894,9 @@ static int nvme_tcp_process_nvme_cqe(struct nvme_tcp_queue *queue,
  	if (req->status == cpu_to_le16(NVME_SC_SUCCESS))
  		req->status = cqe->status;
  
-	if (!nvme_try_complete_req(rq, req->status, cqe->result))
-		nvme_complete_rq(rq);
+	nvme_tcp_complete_request(rq, req->status, cqe->result,
+				  cqe->command_id);
  	queue->nr_cqe++;
-
  	return 0;
  }
  

@@ -998,10 +1094,13 @@ static int nvme_tcp_recv_pdu(struct nvme_tcp_queue *queue, struct sk_buff *skb,
  
  static inline void nvme_tcp_end_request(struct request *rq, u16 status)
  {
+	struct nvme_tcp_request *req = blk_mq_rq_to_pdu(rq);
+	struct nvme_tcp_queue *queue = req->queue;
+	struct nvme_tcp_data_pdu *pdu = (void *)queue->pdu;
  	union nvme_result res = {};
  
-	if (!nvme_try_complete_req(rq, cpu_to_le16(status << 1), res))
-		nvme_complete_rq(rq);
+	nvme_tcp_complete_request(rq, cpu_to_le16(status << 1), res,
+				  pdu->command_id);
  }
  
  static int nvme_tcp_recv_data(struct nvme_tcp_queue *queue, struct sk_buff *skb,

@@ -1308,6 +1407,15 @@ static int nvme_tcp_try_send_cmd_pdu(struct nvme_tcp_request *req)
  	else
  		msg.msg_flags |= MSG_EOR;
  
+	if (test_bit(NVME_TCP_Q_OFF_DDP, &queue->flags)) {
+		ret = nvme_tcp_setup_ddp(queue, pdu->cmd.common.command_id,
+					 blk_mq_rq_from_pdu(req));
+		WARN_ONCE(ret, "ddp setup failed (queue 0x%x, cid 0x%x, ret=%d)",
+			  nvme_tcp_queue_id(queue),
+			  pdu->cmd.common.command_id,
+			  ret);
+	}

+
  	if (queue->hdr_digest && !req->offset)
  		nvme_tcp_hdgst(queue->snd_hash, pdu, sizeof(*pdu));
  

@@ -2739,6 +2847,9 @@ static blk_status_t nvme_tcp_setup_cmd_pdu(struct nvme_ns *ns,
  	if (ret)
  		return ret;
  
+#ifdef CONFIG_ULP_DDP
+	req->offloaded = false;
+#endif
  	req->state = NVME_TCP_SEND_CMD_PDU;
  	req->status = cpu_to_le16(NVME_SC_SUCCESS);
  	req->offset = 0;