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Subject[PATCH AUTOSEL 5.5 21/28] nvmet-tcp: set MSG_MORE only if we actually have more to send
Date
From: Sagi Grimberg <sagi@grimberg.me>

[ Upstream commit 98fd5c723730f560e5bea919a64ac5b83d45eb72 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 af674fc0bb1e4..5bb5342b8d0c7 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;
}
--
2.20.1
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