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

Cornelia Huck
2020-04-08T16:28:08Z

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