From: Uday Shankar <ushankar@purestorage.com>
To: Costa Sapuntzakis <costa@purestorage.com>,
Randy Jennings <randyj@purestorage.com>,
Hannes Reinecke <hare@suse.de>, Sagi Grimberg <sagi@grimberg.me>,
Keith Busch <kbusch@kernel.org>, Christoph Hellwig <hch@lst.de>,
Jens Axboe <axboe@fb.com>
Cc: Uday Shankar <ushankar@purestorage.com>, linux-nvme@lists.infradead.org
Subject: [PATCH v4 3/3] nvme: improve handling of long keep alives
Date: Wed, 24 May 2023 13:38:09 -0600 [thread overview]
Message-ID: <20230524193809.1360269-4-ushankar@purestorage.com> (raw)
In-Reply-To: <20230524193809.1360269-1-ushankar@purestorage.com>
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>
---
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 54f5440a0b83..a4287ae967b2 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1195,6 +1195,20 @@ 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 - nvme_req(rq)->start_time;
+ 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);
@@ -1213,7 +1227,7 @@ 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;
}
--
2.25.1
prev parent reply other threads:[~2023-05-24 19:38 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-24 19:38 [PATCH v4 0/3] keepalive bugfixes Uday Shankar
2023-05-24 19:38 ` [PATCH v4 1/3] nvme: double KA polling frequency to avoid KATO with TBKAS on Uday Shankar
2023-05-24 19:38 ` [PATCH v4 2/3] nvme: check IO start time when deciding to defer KA Uday Shankar
2023-05-24 20:39 ` Keith Busch
2023-05-24 19:38 ` Uday Shankar [this message]
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