Re: [RESEND PATCH] xen/blkfront: convert to blk-mq APIs

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Jul 06, 2015 at 05:56:48PM +0800, Bob Liu wrote:
> From: Arianna Avanzini <avanzini.arianna@gmail.com>
> 
> This patch converts xen-blkfront driver to use the block multiqueue APIs.
> Only one hardware queue is used now, so there is no performance change.
> 
> The legacy non-mq code was deleted completely which is the same as other drivers
> like virtio, mtip, and nvme.
> 
> Also dropped unnecessary holding of info->io_lock when calling into blk-mq APIs.

Yeey!

Two points:

 - The io_lock is now used to guard against concurrent access to the ring.
   We should rename it to 'ring_lock'.

 - The kick_pending_request_queues should have an extra argument - 'bool locked'.
   This is so that you don't drop and immediately grab the lock from the blkif_interrupt.

   See:

> @@ -1243,9 +1243,8 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>  	} else
>  		info->ring.sring->rsp_event = i + 1;
>  
> -	kick_pending_request_queues(info);
> -
>  	spin_unlock_irqrestore(&info->io_lock, flags);
> +	kick_pending_request_queues(info);
>  
>  	return IRQ_HANDLED;
>  }

Otherwise Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>