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

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Message-ID: <20200408182750.6d9443f6.cohuck@redhat.com>
Date:   Wed, 8 Apr 2020 18:27:50 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ux.ibm.com, borntraeger@...ibm.com,
        mjrosato@...ux.ibm.com, pmorel@...ux.ibm.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        jjherne@...ux.ibm.com, fiuczy@...ux.ibm.com
Subject: Re: [PATCH v7 01/15] s390/vfio-ap: store queue struct in hash table
 for quick access

On Wed, 8 Apr 2020 11:38:07 -0400
Tony Krowiak <akrowiak@...ux.ibm.com> wrote:

> On 4/8/20 6:48 AM, Cornelia Huck wrote:
> > On Tue,  7 Apr 2020 15:20:01 -0400
> > Tony Krowiak <akrowiak@...ux.ibm.com> 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@...ux.ibm.com>
> >> ---
> >>   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(-)
> >>  
> > (...)

> >> - */
> >> -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.

Thanks for the explanation, that makes sense.

> 
> >  
> >> -
> >> -	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.

Ok, so anything further is not needed.

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

Looks good to me, then. With vfio_ap_get_queue made static and the
kerneldoc restored/updated:

Reviewed-by: Cornelia Huck <cohuck@...hat.com>