Re: [PATCH v7 01/15] s390/vfio-ap: store queue struct in hash table for quick access

[Tony Krowiak]

On 4/8/20 6:48 AM, Cornelia Huck wrote:
> On Tue,  7 Apr 2020 15:20:01 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > Rather than looping over potentially 65535 objects, let's store the
> > structures for caching information about queue devices bound to the
> > vfio_ap device driver in a hash table keyed by APQN.
> This also looks like a nice code simplification.
>
> > Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> > ---
> >   drivers/s390/crypto/vfio_ap_drv.c     | 28 +++------
> >   drivers/s390/crypto/vfio_ap_ops.c     | 90 ++++++++++++++-------------
> >   drivers/s390/crypto/vfio_ap_private.h | 10 ++-
> >   3 files changed, 60 insertions(+), 68 deletions(-)
> (...)
>
> > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> > index 5c0f53c6dde7..134860934fe7 100644
> > --- a/drivers/s390/crypto/vfio_ap_ops.c
> > +++ b/drivers/s390/crypto/vfio_ap_ops.c
> > @@ -26,45 +26,16 @@
> >   
> >   static int vfio_ap_mdev_reset_queues(struct mdev_device *mdev);
> >   
> > -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
> > - * @apqn: The queue APQN
> > - *
> > - * Retrieve a queue with a specific APQN from the list of the
> > - * devices of the vfio_ap_drv.
> > - * Verify that the APID and the APQI are set in the matrix.
> > - *
> > - * Returns the pointer to the associated vfio_ap_queue
> Any reason you're killing this comment, instead of adapting it? The
> function is even no longer static...

I can update and restore the comment and the function should be static.

> > - */
> > -static struct vfio_ap_queue *vfio_ap_get_queue(
> > -					struct ap_matrix_mdev *matrix_mdev,
> > -					int apqn)
> > +struct vfio_ap_queue *vfio_ap_get_queue(unsigned long apqn)
> >   {
> >   	struct vfio_ap_queue *q;
> > -	struct device *dev;
> > -
> > -	if (!test_bit_inv(AP_QID_CARD(apqn), matrix_mdev->matrix.apm))
> > -		return NULL;
> > -	if (!test_bit_inv(AP_QID_QUEUE(apqn), matrix_mdev->matrix.aqm))
> > -		return NULL;
> These were just optimizations and therefore can be dropped now?

The purpose of this function has changed from its previous incarnation.
This function was originally called from the handle_pqap() function and
served two purposes: It retrieved the struct vfio_ap_queue as driver data
and linked the matrix_mdev to the vfio_ap_queue. The linking of the
matrix_mdev and the vfio_ap_queue are now done when queue devices
are probed and when adapters and domains are assigned; so now, the
handle_pqap() function calls this function to retrieve both the
vfio_ap_queue as well as the matrix_mdev to which it is linked. 
Consequently,
the above code is no longer needed.

> > -
> > -	dev = driver_find_device(&matrix_dev->vfio_ap_drv->driver, NULL,
> > -				 &apqn, match_apqn);
> > -	if (!dev)
> > -		return NULL;
> > -	q = dev_get_drvdata(dev);
> > -	q->matrix_mdev = matrix_mdev;
> > -	put_device(dev);
> >   
> > -	return q;
> > +	hash_for_each_possible(matrix_dev->qtable, q, qnode, apqn) {
> > +		if (q && (apqn == q->apqn))
> > +			return q;
> > +	}
> Do we need any serialization here? Previously, the driver core made
> sure we could get a reference only if the device was still registered;
> not sure if we need any further guarantees now.

The vfio_ap_queue structs are created when the queue device is
probed and removed when the queue device is removed.

> > +
> > +	return NULL;
> >   }
> >   
> >   /**
> (...)