From: Uday Shankar ushankar@purestorage.com
[ 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@purestorage.com Reported-by: Randy Jennings randyj@purestorage.com Signed-off-by: Uday Shankar ushankar@purestorage.com Reviewed-by: Hannes Reinecke hare@suse.de Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Keith Busch kbusch@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- 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 06dd1c0780bfc..4e4203c327114 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -1234,6 +1234,20 @@ 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);
@@ -1252,7 +1266,7 @@ 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; }