From: Uday Shankar <ushankar@xxxxxxxxxxxxxxx>
[ Upstream commit c7275ce6a5fd32ca9f5a6294ed89cf0523181af9 ]
Upon keep alive completion, nvme_keep_alive_work is scheduled with the
same delay every time. If keep alive commands are completing slowly,
this may cause a keep alive timeout. The following trace illustrates the
issue, taking KATO = 8 and TBKAS off for simplicity:
1. t = 0: run nvme_keep_alive_work, send keep alive
2. t = ε: keep alive reaches controller, controller restarts its keep
alive timer
3. t = 4: host receives keep alive completion, schedules
nvme_keep_alive_work with delay 4
4. t = 8: run nvme_keep_alive_work, send keep alive
Here, a keep alive having RTT of 4 causes a delay of at least 8 - ε
between the controller receiving successive keep alives. With ε small,
the controller is likely to detect a keep alive timeout.
Fix this by calculating the RTT of the keep alive command, and adjusting
the scheduling delay of the next keep alive work accordingly.
Reported-by: Costa Sapuntzakis <costa@xxxxxxxxxxxxxxx>
Reported-by: Randy Jennings <randyj@xxxxxxxxxxxxxxx>
Signed-off-by: Uday Shankar <ushankar@xxxxxxxxxxxxxxx>
Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/nvme/host/core.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index d87b8dfda622a..8a632bf7f5a8f 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1199,6 +1199,20 @@ static enum rq_end_io_ret nvme_keep_alive_end_io(struct request *rq,
struct nvme_ctrl *ctrl = rq->end_io_data;
unsigned long flags;
bool startka = false;
+ unsigned long rtt = jiffies - (rq->deadline - rq->timeout);
+ unsigned long delay = nvme_keep_alive_work_period(ctrl);
+
+ /*
+ * Subtract off the keepalive RTT so nvme_keep_alive_work runs
+ * at the desired frequency.
+ */
+ if (rtt <= delay) {
+ delay -= rtt;
+ } else {
+ dev_warn(ctrl->device, "long keepalive RTT (%u ms)\n",
+ jiffies_to_msecs(rtt));
+ delay = 0;
+ }
blk_mq_free_request(rq);
@@ -1217,7 +1231,7 @@ static enum rq_end_io_ret nvme_keep_alive_end_io(struct request *rq,
startka = true;
spin_unlock_irqrestore(&ctrl->lock, flags);
if (startka)
- nvme_queue_keep_alive_work(ctrl);
+ queue_delayed_work(nvme_wq, &ctrl->ka_work, delay);
return RQ_END_IO_NONE;
}
--
2.39.2
