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author | Uday Shankar <ushankar@purestorage.com> | 2023-05-25 21:22:02 +0300 |
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committer | Keith Busch <kbusch@kernel.org> | 2023-05-30 19:20:44 +0300 |
commit | ea4d453b9ec9ea279c39744cd0ecb47ef48ede35 (patch) | |
tree | 307acbc6cdb01d719c723c1d9c55a76f68a328ce /drivers/nvme/host | |
parent | 31a5978243d24d77be4bacca56c78a0fbc43b00d (diff) | |
download | linux-ea4d453b9ec9ea279c39744cd0ecb47ef48ede35.tar.xz |
nvme: double KA polling frequency to avoid KATO with TBKAS on
With TBKAS on, the completion of one command can defer sending a
keep alive for up to twice the delay between successive runs of
nvme_keep_alive_work. The current delay of KATO / 2 thus makes it
possible for one command to defer sending a keep alive for up to
KATO, which can result in the controller detecting a KATO. The following
trace demonstrates the issue, taking KATO = 8 for simplicity:
1. t = 0: run nvme_keep_alive_work, no keep-alive sent
2. t = ε: I/O completion seen, set comp_seen = true
3. t = 4: run nvme_keep_alive_work, see comp_seen == true,
skip sending keep-alive, set comp_seen = false
4. t = 8: run nvme_keep_alive_work, see comp_seen == false,
send a keep-alive command.
Here, there is a delay of 8 - ε between receiving a command completion
and sending the next command. With ε small, the controller is likely to
detect a keep alive timeout.
Fix this by running nvme_keep_alive_work with a delay of KATO / 4
whenever TBKAS is on. Going through the above trace now gives us a
worst-case delay of 4 - ε, which is in line with the recommendation of
sending a command every KATO / 2 in the NVMe specification.
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: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Diffstat (limited to 'drivers/nvme/host')
-rw-r--r-- | drivers/nvme/host/core.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c index c6cba1cc101c..6417c7928fa3 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -1163,9 +1163,25 @@ EXPORT_SYMBOL_NS_GPL(nvme_passthru_end, NVME_TARGET_PASSTHRU); * The host should send Keep Alive commands at half of the Keep Alive Timeout * accounting for transport roundtrip times [..]. */ +static unsigned long nvme_keep_alive_work_period(struct nvme_ctrl *ctrl) +{ + unsigned long delay = ctrl->kato * HZ / 2; + + /* + * When using Traffic Based Keep Alive, we need to run + * nvme_keep_alive_work at twice the normal frequency, as one + * command completion can postpone sending a keep alive command + * by up to twice the delay between runs. + */ + if (ctrl->ctratt & NVME_CTRL_ATTR_TBKAS) + delay /= 2; + return delay; +} + static void nvme_queue_keep_alive_work(struct nvme_ctrl *ctrl) { - queue_delayed_work(nvme_wq, &ctrl->ka_work, ctrl->kato * HZ / 2); + queue_delayed_work(nvme_wq, &ctrl->ka_work, + nvme_keep_alive_work_period(ctrl)); } static enum rq_end_io_ret nvme_keep_alive_end_io(struct request *rq, |