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

Tony Krowiak
2020-04-08T16:34:23Z

On 4/8/20 12:27 PM, Cornelia Huck wrote:
> 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:

Already done, thanks for the review.

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