Re: [PATCH v5 3/6] nvme-tcp: short-circuit reconnect retries

From: Sagi Grimberg
Date: Tue Apr 09 2024 - 16:40:24 EST




On 09/04/2024 12:35, Daniel Wagner wrote:
From: Hannes Reinecke <hare@xxxxxxx>

Returning an nvme status from nvme_tcp_setup_ctrl() indicates that the
association was established and we have received a status from the
controller; consequently we should honour the DNR bit. If not any future
reconnect attempts will just return the same error, so we can
short-circuit the reconnect attempts and fail the connection directly.

Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
[dwagner: add helper to decide to reconnect]
Signed-off-by: Daniel Wagner <dwagner@xxxxxxx>
---
drivers/nvme/host/nvme.h | 24 ++++++++++++++++++++++++
drivers/nvme/host/tcp.c | 23 +++++++++++++++--------
2 files changed, 39 insertions(+), 8 deletions(-)

diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 9b8904a476b8..dfe103283a3d 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -701,6 +701,30 @@ static inline bool nvme_is_path_error(u16 status)
return (status & 0x700) == 0x300;
}
+/*
+ * Evaluate the status information returned by the LLDD

We usually say transport, less so LLDD.

in order to
+ * decided if a reconnect attempt should be scheduled.
+ *
+ * There are two cases where no reconnect attempt should be attempted:
+ *
+ * 1) The LLDD reports an negative status. There was an error (e.g. no
+ * memory) on the host side and thus abort the operation.
+ * Note, there are exception such as ENOTCONN which is
+ * not an internal driver error, thus we filter these errors
+ * out and retry later.

What is this ENOTCONN here? From what I see its just a random
escape value to bypass the status check. I think that 0 would do the same
wouldn't it?

+ * 2) The DNR bit is set and the specification states no further
+ * connect attempts with the same set of paramenters should be
+ * attempted.
+ */
+static inline bool nvme_ctrl_reconnect(int status)
+{
+ if (status < 0 && status != -ENOTCONN)
+ return false;
+ else if (status > 0 && (status & NVME_SC_DNR))
+ return false;
+ return true;
+}
+
/*
* Fill in the status and result information from the CQE, and then figure out
* if blk-mq will need to use IPI magic to complete the request, and if yes do
diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index fdbcdcedcee9..7e25a96e9870 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -2155,9 +2155,11 @@ static void nvme_tcp_teardown_io_queues(struct nvme_ctrl *ctrl,
nvme_tcp_destroy_io_queues(ctrl, remove);
}
-static void nvme_tcp_reconnect_or_remove(struct nvme_ctrl *ctrl)
+static void nvme_tcp_reconnect_or_remove(struct nvme_ctrl *ctrl,
+ int status)
{
enum nvme_ctrl_state state = nvme_ctrl_state(ctrl);
+ bool recon = nvme_ctrl_reconnect(status);
/* If we are resetting/deleting then do nothing */
if (state != NVME_CTRL_CONNECTING) {
@@ -2165,13 +2167,14 @@ static void nvme_tcp_reconnect_or_remove(struct nvme_ctrl *ctrl)
return;
}
- if (nvmf_should_reconnect(ctrl)) {
+ if (recon && nvmf_should_reconnect(ctrl)) {

its weird to have a condition that checks _and_ condition
of two different "should reconnect" conditions.

Why don't we simply pass the status to nvmf_should_reconnect()
and evaluate there?

dev_info(ctrl->device, "Reconnecting in %d seconds...\n",
ctrl->opts->reconnect_delay);
queue_delayed_work(nvme_wq, &to_tcp_ctrl(ctrl)->connect_work,
ctrl->opts->reconnect_delay * HZ);
} else {
- dev_info(ctrl->device, "Removing controller...\n");
+ dev_info(ctrl->device, "Removing controller (%d)...\n",
+ status);
nvme_delete_ctrl(ctrl);
}
}
@@ -2252,10 +2255,12 @@ static void nvme_tcp_reconnect_ctrl_work(struct work_struct *work)
struct nvme_tcp_ctrl *tcp_ctrl = container_of(to_delayed_work(work),
struct nvme_tcp_ctrl, connect_work);
struct nvme_ctrl *ctrl = &tcp_ctrl->ctrl;
+ int ret;
++ctrl->nr_reconnects;
- if (nvme_tcp_setup_ctrl(ctrl, false))
+ ret = nvme_tcp_setup_ctrl(ctrl, false);
+ if (ret)
goto requeue;
dev_info(ctrl->device, "Successfully reconnected (%d attempt)\n",
@@ -2268,7 +2273,7 @@ static void nvme_tcp_reconnect_ctrl_work(struct work_struct *work)
requeue:
dev_info(ctrl->device, "Failed reconnect attempt %d\n",
ctrl->nr_reconnects);
- nvme_tcp_reconnect_or_remove(ctrl);
+ nvme_tcp_reconnect_or_remove(ctrl, ret);
}
static void nvme_tcp_error_recovery_work(struct work_struct *work)
@@ -2295,7 +2300,7 @@ static void nvme_tcp_error_recovery_work(struct work_struct *work)
return;
}
- nvme_tcp_reconnect_or_remove(ctrl);
+ nvme_tcp_reconnect_or_remove(ctrl, -ENOTCONN);
}
static void nvme_tcp_teardown_ctrl(struct nvme_ctrl *ctrl, bool shutdown)
@@ -2315,6 +2320,7 @@ static void nvme_reset_ctrl_work(struct work_struct *work)
{
struct nvme_ctrl *ctrl =
container_of(work, struct nvme_ctrl, reset_work);
+ int ret;
nvme_stop_ctrl(ctrl);
nvme_tcp_teardown_ctrl(ctrl, false);
@@ -2328,14 +2334,15 @@ static void nvme_reset_ctrl_work(struct work_struct *work)
return;
}
- if (nvme_tcp_setup_ctrl(ctrl, false))
+ ret = nvme_tcp_setup_ctrl(ctrl, false);
+ if (ret)
goto out_fail;
return;
out_fail:
++ctrl->nr_reconnects;
- nvme_tcp_reconnect_or_remove(ctrl);
+ nvme_tcp_reconnect_or_remove(ctrl, ret);
}
static void nvme_tcp_stop_ctrl(struct nvme_ctrl *ctrl)