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

[JeffleXu]

Any comments?

On 9/22/20 12:28 PM, Jeffle Xu wrote:
> 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;
>   	}