Commit 774a9636 authored by Uday Shankar's avatar Uday Shankar Committed by Keith Busch
Browse files

nvme: check IO start time when deciding to defer KA 



When a command completes, we set a flag which will skip sending a
keep alive at the next run of nvme_keep_alive_work when TBKAS is on.
However, if the command was submitted long ago, it's possible that
the controller may have also restarted its keep alive timer (as a
result of receiving the command) long ago. The following trace
demonstrates the issue, assuming TBKAS is on and KATO = 8 for
simplicity:

1. t = 0: submit I/O commands A, B, C, D, E
2. t = 0.5: commands A, B, C, D, E reach controller, restart its keep
            alive timer
3. t = 1: A completes
4. t = 2: run nvme_keep_alive_work, see recent completion, do nothing
5. t = 3: B completes
6. t = 4: run nvme_keep_alive_work, see recent completion, do nothing
7. t = 5: C completes
8. t = 6: run nvme_keep_alive_work, see recent completion, do nothing
9. t = 7: D completes
10. t = 8: run nvme_keep_alive_work, see recent completion, do nothing
11. t = 9: E completes

At this point, 8.5 seconds have passed without restarting the
controller's keep alive timer, so the controller will detect a keep
alive timeout.

Fix this by checking the IO start time when deciding to defer sending a
keep alive command. Only set comp_seen if the command started after the
most recent run of nvme_keep_alive_work. With this change, the
completions of B, C, and D will not set comp_seen and the run of
nvme_keep_alive_work at t = 4 will send a keep alive.

Reported-by: default avatarCosta Sapuntzakis <costa@purestorage.com>
Reported-by: default avatarRandy Jennings <randyj@purestorage.com>
Signed-off-by: default avatarUday Shankar <ushankar@purestorage.com>
Reviewed-by: default avatarHannes Reinecke <hare@suse.de>
Reviewed-by: default avatarSagi Grimberg <sagi@grimberg.me>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarKeith Busch <kbusch@kernel.org>
parent ea4d453b

drivers/nvme/host/core.c

+13 −1
Original line number Diff line number Diff line
@@ -397,7 +397,16 @@ void nvme_complete_rq(struct request *req) 
	trace_nvme_complete_rq(req);

	nvme_cleanup_cmd(req);



	if (ctrl->kas)

	/*

	 * Completions of long-running commands should not be able to

	 * defer sending of periodic keep alives, since the controller

	 * may have completed processing such commands a long time ago

	 * (arbitrarily close to command submission time).

	 * req->deadline - req->timeout is the command submission time

	 * in jiffies.

	 */

	if (ctrl->kas &&

	    req->deadline - req->timeout >= ctrl->ka_last_check_time)

		ctrl->comp_seen = true;



	switch (nvme_decide_disposition(req)) {
@@ -1200,6 +1209,7 @@ static enum rq_end_io_ret nvme_keep_alive_end_io(struct request *rq, 
		return RQ_END_IO_NONE;

	}



	ctrl->ka_last_check_time = jiffies;

	ctrl->comp_seen = false;

	spin_lock_irqsave(&ctrl->lock, flags);

	if (ctrl->state == NVME_CTRL_LIVE ||
@@ -1218,6 +1228,8 @@ static void nvme_keep_alive_work(struct work_struct *work) 
	bool comp_seen = ctrl->comp_seen;

	struct request *rq;



	ctrl->ka_last_check_time = jiffies;



	if ((ctrl->ctratt & NVME_CTRL_ATTR_TBKAS) && comp_seen) {

		dev_dbg(ctrl->device,

			"reschedule traffic based keep-alive timer\n");

drivers/nvme/host/nvme.h

+1 −0
Original line number Diff line number Diff line
@@ -328,6 +328,7 @@ struct nvme_ctrl { 
	struct delayed_work ka_work;

	struct delayed_work failfast_work;

	struct nvme_command ka_cmd;

	unsigned long ka_last_check_time;

	struct work_struct fw_act_work;

	unsigned long events;