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: <20200427171739.76291a74.pasic@linux.ibm.com>
Date:   Mon, 27 Apr 2020 17:17:39 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Harald Freudenberger <freude@...ux.ibm.com>
Cc:     Tony Krowiak <akrowiak@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        borntraeger@...ibm.com, cohuck@...hat.com, mjrosato@...ux.ibm.com,
        pmorel@...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 Mon, 27 Apr 2020 15:05:23 +0200
Harald Freudenberger <freude@...ux.ibm.com> wrote:

> On 24.04.20 05:57, Halil Pasic 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.  
> > @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?


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.