Commit a15573c4 authored Feb 22, 2016 by Daniel Verkamp

nvme: don't reset already-disabled controllers



In nvme_ctrlr_hw_reset(), if we encounter a controller whose CC.EN bit
is already 0 (controller is disabled), the previous code would enable
the controller just so that it could be disabled to get a full reset
(transition from CC.EN = 1 to CC.EN = 0).  However, it is a safe
assumption that if CC.EN is already 0, the controller has just been
reset, so we don't need to reset it again.

This saves a significant amount of time (2+ seconds per controller with
Intel SSD DC P3700) during initialization for devices that were disabled
on startup.

Change-Id: I552b1f0f185a84a8a0ce57a93b012d9d5fe096f3
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>

parent 4cb05719

lib/nvme/nvme_ctrlr.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -394,11 +394,11 @@ nvme_ctrlr_hw_reset(struct spdk_nvme_ctrlr *ctrlr)
		}
		} else {
		/*
		* Ensure we do a transition from cc.en==1 to cc.en==0.
		* If we started disabled (cc.en==0), then we have to enable
		* first to get a reset.
		* The controller was already disabled. We will assume that nothing
		* has been changed since cc.en was set to 0,
		* meaning that we don't need to do an extra reset, and we can just
		* re-enable the controller.
		*/
		nvme_ctrlr_enable(ctrlr);
		}

		nvme_ctrlr_disable(ctrlr);