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: <6ea12752-d23f-abe4-8d5f-3e7738984576@linux.ibm.com>
Date:   Mon, 27 Apr 2020 17:48:58 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>,
        Harald Freudenberger <freude@...ux.ibm.com>
Cc:     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 4/27/20 11:17 AM, Halil Pasic wrote:
> 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?

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.
>
>
>