[PATCH v2 1/2] nvmet-tcp: set MSG_MORE only if we actually have more to send

[PATCH v2 1/2] nvmet-tcp: set MSG_MORE only if we actually have more to send

[Sagi Grimberg]

When we send PDU data, we want to optimize the tcp stack
operation if we have more data to send. So when we set MSG_MORE
when:
- We have more fragments coming in the batch, or
- We have a more data to send in this PDU
- We don't have a data digest trailer
- We optimize with the SUCCESS flag and omit the NVMe completion
  (used if sq_head pointer update is disabled)

This addresses a regression in QD=1 with SUCCESS flag optimization
as we unconditionally set MSG_MORE when we didn't actually have
more data to send.

Fixes: 70583295388a ("nvmet-tcp: implement C2HData SUCCESS optimization")
Reported-by: Mark Wunderlich <mark.wunderlich@intel.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
---
- No changes from v1

 drivers/nvme/target/tcp.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/target/tcp.c b/drivers/nvme/target/tcp.c
index 1f4322ee7dbe..e5d000f12059 100644
--- a/drivers/nvme/target/tcp.c
+++ b/drivers/nvme/target/tcp.c
@@ -525,7 +525,7 @@ static int nvmet_try_send_data_pdu(struct nvmet_tcp_cmd *cmd)
 	return 1;
 }
 
-static int nvmet_try_send_data(struct nvmet_tcp_cmd *cmd)
+static int nvmet_try_send_data(struct nvmet_tcp_cmd *cmd, bool last_in_batch)
 {
 	struct nvmet_tcp_queue *queue = cmd->queue;
 	int ret;
@@ -533,9 +533,15 @@ static int nvmet_try_send_data(struct nvmet_tcp_cmd *cmd)
 	while (cmd->cur_sg) {
 		struct page *page = sg_page(cmd->cur_sg);
 		u32 left = cmd->cur_sg->length - cmd->offset;
+		int flags = MSG_DONTWAIT;
+
+		if ((!last_in_batch && cmd->queue->send_list_len) ||
+		    cmd->wbytes_done + left < cmd->req.transfer_len ||
+		    queue->data_digest || !queue->nvme_sq.sqhd_disabled)
+			flags |= MSG_MORE;
 
 		ret = kernel_sendpage(cmd->queue->sock, page, cmd->offset,
-					left, MSG_DONTWAIT | MSG_MORE);
+					left, flags);
 		if (ret <= 0)
 			return ret;
 
@@ -666,7 +672,7 @@ static int nvmet_tcp_try_send_one(struct nvmet_tcp_queue *queue,
 	}
 
 	if (cmd->state == NVMET_TCP_SEND_DATA) {
-		ret = nvmet_try_send_data(cmd);
+		ret = nvmet_try_send_data(cmd, last_in_batch);
 		if (ret <= 0)
 			goto done_send;
 	}
-- 
2.20.1


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[PATCH v2 2/2] nvmet-tcp: optimize tcp stack TX when data digest is used

[Sagi Grimberg]

If we have a 4-byte data digest to send to the wire, but we
have more data to send, set MSG_MORE to tell the stack
that more is coming.

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
---
Changes from v1:
- fix compilation error

 drivers/nvme/target/tcp.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/target/tcp.c b/drivers/nvme/target/tcp.c
index e5d000f12059..f4de7b075284 100644
--- a/drivers/nvme/target/tcp.c
+++ b/drivers/nvme/target/tcp.c
@@ -628,7 +628,7 @@ static int nvmet_try_send_r2t(struct nvmet_tcp_cmd *cmd, bool last_in_batch)
 	return 1;
 }
 
-static int nvmet_try_send_ddgst(struct nvmet_tcp_cmd *cmd)
+static int nvmet_try_send_ddgst(struct nvmet_tcp_cmd *cmd, bool last_in_batch)
 {
 	struct nvmet_tcp_queue *queue = cmd->queue;
 	struct msghdr msg = { .msg_flags = MSG_DONTWAIT };
@@ -638,6 +638,9 @@ static int nvmet_try_send_ddgst(struct nvmet_tcp_cmd *cmd)
 	};
 	int ret;
 
+	if (!last_in_batch && cmd->queue->send_list_len)
+		msg.msg_flags |= MSG_MORE;
+
 	ret = kernel_sendmsg(queue->sock, &msg, &iov, 1, iov.iov_len);
 	if (unlikely(ret <= 0))
 		return ret;
@@ -678,7 +681,7 @@ static int nvmet_tcp_try_send_one(struct nvmet_tcp_queue *queue,
 	}
 
 	if (cmd->state == NVMET_TCP_SEND_DDGST) {
-		ret = nvmet_try_send_ddgst(cmd);
+		ret = nvmet_try_send_ddgst(cmd, last_in_batch);
 		if (ret <= 0)
 			goto done_send;
 	}
-- 
2.20.1


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RE: [PATCH v2 1/2] nvmet-tcp: set MSG_MORE only if we actually have more to send

[Wunderlich, Mark]

> When we send PDU data, we want to optimize the tcp stack operation if we have more data to send. So when we set MSG_MORE
> when:
> - We have more fragments coming in the batch, or
> - We have a more data to send in this PDU
> - We don't have a data digest trailer
> - We optimize with the SUCCESS flag and omit the NVMe completion
>   (used if sq_head pointer update is disabled)

> This addresses a regression in QD=1 with SUCCESS flag optimization as we unconditionally set MSG_MORE when we didn't actually have more data to send.

> Fixes: 70583295388a ("nvmet-tcp: implement C2HData SUCCESS optimization")
> Reported-by: Mark Wunderlich <mark.wunderlich@intel.com>
> Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
> ---

Tested-by: Mark Wunderlich <mark.wunderlich@intel.com>


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RE: [PATCH v2 2/2] nvmet-tcp: optimize tcp stack TX when data digest is used

[Wunderlich, Mark]

> Subject: [PATCH v2 2/2] nvmet-tcp: optimize tcp stack TX when data digest is used

> If we have a 4-byte data digest to send to the wire, but we have more data to send, set MSG_MORE to tell the stack that more is coming.

> Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
> ---
> Changes from v1:
> - fix compilation error

Looks good now.
Reviewed-by: Mark Wunderlich <mark.wunderlich@intel.com>




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