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

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Message-ID: <20150710195714.GB31146@l.oracle.com>
Date:	Fri, 10 Jul 2015 15:57:14 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Bob Liu <bob.liu@...cle.com>
Cc:	linux-kernel@...r.kernel.org, axboe@...com, hch@...radead.org,
	xen-devel@...ts.xenproject.org, avanzini.arianna@...il.com,
	david.vrabel@...rix.com, marcus.granado@...rix.com,
	roger.pau@...rix.com
Subject: Re: [RESEND PATCH] xen/blkfront: convert to blk-mq APIs

On Mon, Jul 06, 2015 at 05:56:48PM +0800, Bob Liu wrote:
> From: Arianna Avanzini <avanzini.arianna@...il.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@...cle.com>
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