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

[Tony Krowiak]

On 4/27/20 11:17 AM, Halil Pasic wrote:
> On Mon, 27 Apr 2020 15:05:23 +0200
> Harald Freudenberger <freude@xxxxxxxxxxxxx> wrote:
>
> > On 24.04.20 05:57, Halil Pasic 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.
> > > @Harald:
> > > Would it make sense to make the efficient lookup of an apqueue base
> > > on its APQN core AP functionality instead of each driver figuring it out
> > > on it's own?
> > >
> > > If I'm not wrong the zcrypt device/driver(s) must the problem of
> > > looking up a queue based on its APQN as well.
> > >
> > > For instance struct ep11_cprb has a target_id filed
> > > (arch/s390/include/uapi/asm/zcrypt.h).
> > >
> > > Regards,
> > > Halil
> > Hi Halil
> >
> > no, the zcrypt drivers don't have this problem. They build up their own device object which
> > includes a pointer to the base ap device.
> I'm a bit confused. Doesn't your code loop first trough the ap_card
> objects to find the APID portion of the APQN, and then loop the queue
> list of the matching card to find the right ap_queue object? Or did I
> miss something? Isn't that what _zcrypt_send_ep11_cprb() does? Can you
> point me to the code that avoids the lookup (by apqn) for zcrypt?

The code you reference, _zcrypt_send_ep11_cprb(), does loop through
each queue associated with each card, but it doesn't appear to be 
looking for
a queue with a particular APQN. It appears to be looking for a queue
meeting a specific set of conditions. At least that's my take after 
taking a very
brief look at the code, so I'm not sure that applies here.

> If you look at the new function of vfio_ap_get_queue(unsigned long apqn)
> it basically about finding the queue based on the apqn, with the
> difference that it is vfio specific.
>
> Regards,
> Halil
>
> > However, this is not a big issue, as the ap_bus holds a list of ap_card objects and within each
> > ap_card object there exists a list of ap_queues.