From: Sagi Grimberg <sagi@grimberg.me>

Date: Thu, 12 Mar 2020 16:06:38 -0700

Subject: [PATCH] nvmet-tcp: set MSG_MORE only if we actually have more to send

Git-commit: 98fd5c723730f560e5bea919a64ac5b83d45eb72

Patch-mainline: v5.6-rc7

References: bsc#1161930

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>

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

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

Signed-off-by: Keith Busch <kbusch@kernel.org>

Acked-by: Hannes Reinecke <hare@suse.com>

---

 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 af674fc0bb1e..5bb5342b8d0c 100644

--- a/drivers/nvme/target/tcp.c

+++ b/drivers/nvme/target/tcp.c

@@ -515,7 +515,7 @@ 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;

@@ -523,9 +523,15 @@ 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;

@@ -660,7 +666,7 @@ 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;

 	}

-- 

2.16.4