linux-kernel - Re: [PATCH v16 02/14] s390/vfio-ap: use new AP bus interface to search for queue devices

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Date:   Wed, 9 Jun 2021 09:52:29 -0400
From:   "Jason J. Herne" <jjherne@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     freude@...ux.ibm.com, borntraeger@...ibm.com, cohuck@...hat.com,
        mjrosato@...ux.ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        fiuczy@...ux.ibm.com
Subject: Re: [PATCH v16 02/14] s390/vfio-ap: use new AP bus interface to
 search for queue devices

On 5/10/21 12:44 PM, Tony Krowiak wrote:
> This patch refactors the vfio_ap device driver to use the AP bus's
> ap_get_qdev() function to retrieve the vfio_ap_queue struct containing
> information about a queue that is bound to the vfio_ap device driver.
> The bus's ap_get_qdev() function retrieves the queue device from a
> hashtable keyed by APQN. This is much more efficient than looping over
> the list of devices attached to the AP bus by several orders of
> magnitude.
> 
> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> Reviewed-by: Halil Pasic <pasic@...ux.ibm.com>
> ---
>   drivers/s390/crypto/vfio_ap_ops.c | 23 +++++++++--------------
>   1 file changed, 9 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index 757166da947e..8a50aa650b65 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -27,13 +27,6 @@
>   static int vfio_ap_mdev_reset_queues(struct mdev_device *mdev);
>   static struct vfio_ap_queue *vfio_ap_find_queue(int apqn);
>   
> -static int match_apqn(struct device *dev, const void *data)
> -{
> -	struct vfio_ap_queue *q = dev_get_drvdata(dev);
> -
> -	return (q->apqn == *(int *)(data)) ? 1 : 0;
> -}
> -
>   /**
>    * vfio_ap_get_queue: Retrieve a queue with a specific APQN from a list
>    * @matrix_mdev: the associated mediated matrix
> @@ -1253,15 +1246,17 @@ static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
>   
>   static struct vfio_ap_queue *vfio_ap_find_queue(int apqn)
>   {
> -	struct device *dev;
> +	struct ap_queue *queue;
>   	struct vfio_ap_queue *q = NULL;

The use of q and queue as variable names was a little confusing to me at first. I tried 
renaming them a few times, the best I could come up with was this:

struct ap_queue *queue;
struct vfio_ap_queue *vfio_queue = NULL;

Take it or leave it :) Other than that, LGTM.
Reviewed-by: Jason J. Herne <jjherne@...ux.ibm.com>


> -	dev = driver_find_device(&matrix_dev->vfio_ap_drv->driver, NULL,
> -				 &apqn, match_apqn);
> -	if (dev) {
> -		q = dev_get_drvdata(dev);
> -		put_device(dev);
> -	}
> +	queue = ap_get_qdev(apqn);
> +	if (!queue)
> +		return NULL;
> +
> +	if (queue->ap_dev.device.driver == &matrix_dev->vfio_ap_drv->driver)
> +		q = dev_get_drvdata(&queue->ap_dev.device);
> +
> +	put_device(&queue->ap_dev.device);
>   
>   	return q;
>   }
> 


-- 
-- Jason J. Herne (jjherne@...ux.ibm.com)