Re: [Xen-devel] [Draft C] Xen on ARM vITS Handling

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

On Mon, Jun 1, 2015 at 5:54 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> On 01/06/15 13:11, Ian Campbell wrote:
>>>> ### Device ID (`ID`)
>>>>
>>>> This parameter is used by commands which manage a specific device and
>>>> the interrupts associated with that device. Checking if a device is
>>>> present and retrieving the data structure must be fast.
>>>>
>>>> The device identifiers may not be assigned contiguously and the maximum
>>>> number is very high (2^32).
>>>>
>>>> XXX In the context of virtualised device ids this may not be the case,
>>>> e.g. we can arrange for (mostly) contiguous device ids and we know the
>>>> bound is significantly lower than 2^32
>>>>
>>>> Possible efficient data structures would be:
>>>>
>>>> 1. List: The lookup/deletion is in O(n) and the insertion will depend
>>>>    if the device should be sorted following their identifier. The
>>>>    memory overhead is 18 bytes per element.
>>>> 2. Red-black tree: All the operations are O(log(n)). The memory
>>>>    overhead is 24 bytes per element.

How about using radix-tree instead of RB-tree?

>>>>
>>>> A Red-black tree seems the more suitable for having fast deviceID
>>>> validation even though the memory overhead is a bit higher compare to
>>>> the list.
>>>
>>> When PHYSDEVOP_pci_device_add is called, memory for its_device structure
>>> and other needed structure for this device is allocated added to RB-tree
>>> with all necessary information
>>
>> Sounds like a reasonable time to do it. I added something based on your
>> words.
>
> Hmmm... The RB-tree suggested is per domain not the host and indexed
> with the vDevID.
>
> This is the only way to know quickly if the domain is able to use the
> device and retrieving a device. Indeed, the vDevID won't be equal to the
> pDevID as the vBDF will be different to the pBDF.

Yes, vBDF is converted to pBDF to match DevID

>
> PHYSDEVOP_pci_device_add is to ask Xen managing the PCI device. At that
> time we don't know to which domain the device will be passthrough.

PHYSDEVOP_pci_device_add will only add its_device to global radix tree list.

When MAPD is received, its_device is removed from global list and added
to per domain list. When domain releases the device, its_device is added back
to global list. is it ok?

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