[RFC] nvme/pci: allocate separate interrupt for reserved non-polled IO queue

[Jeffle Xu]

One queue will be reserved for non-polled IO when nvme.poll_queues is
greater or equal than the number of IO queues that the nvme controller
can provide. Currently the reserved queue for non-polled IO will reuse
the interrupt used by admin queue in this case, e.g, vector 0.

This can work and the performance may not be an issue since the admin
queue is used unfrequently. However this behaviour may be inconsistent
with that when nvme.poll_queues is smaller than the number of IO
queues available.

Thus allocate separate interrupt for this reserved queue, and thus make
the behaviour consistent.

Signed-off-by: Jeffle Xu <jefflexu at linux.alibaba.com>
---
 drivers/nvme/host/pci.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 899d2f4d7ab6..ff3e28a8a9e0 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2042,12 +2042,14 @@ static int nvme_setup_irqs(struct nvme_dev *dev, unsigned int nr_io_queues)
 
 	/*
 	 * Poll queues don't need interrupts, but we need at least one IO
-	 * queue left over for non-polled IO.
+	 * queue left over for non-polled IO. Also one interrupt for admin
+	 * queue.
 	 */
 	this_p_queues = dev->nr_poll_queues;
 	if (this_p_queues >= nr_io_queues) {
 		this_p_queues = nr_io_queues - 1;
-		irq_queues = 1;
+		/* Allocate separate interrupt for reserved non-polled IO queue. */
+		irq_queues = 2;
 	} else {
 		irq_queues = nr_io_queues - this_p_queues + 1;
 	}
-- 
2.27.0