Commit ff7e2122 authored Jan 22, 2016 by Jim Harris Committed by Daniel Verkamp Feb 08, 2016

nvme: reduce number of mmio writes in completion path



Instead of writing the completion doorbell once per completion,
just write it once at the end of the completion while loop.
This reduces the number of mmio writes by coalescing several
writes into one when we get multiple completions at a time.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: I3cc3864dcfe43186bec51be1a732e84ef3be05ae

parent 047c5aaa

lib/nvme/nvme_qpair.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -509,13 +509,15 @@ nvme_qpair_process_completions(struct nvme_qpair *qpair, uint32_t max_completion
		qpair->phase = !qpair->phase;
		}

		spdk_mmio_write_4(qpair->cq_hdbl, qpair->cq_head);

		if (++num_completions == max_completions) {
		break;
		}
		}

		if (num_completions > 0) {
		spdk_mmio_write_4(qpair->cq_hdbl, qpair->cq_head);
		}

		return num_completions;
		}