Re: [PATCH v4 06/11] vpci/header: handle p2m range sets per BAR

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 19.11.21 15:29, Jan Beulich wrote:
> On 19.11.2021 14:19, Oleksandr Andrushchenko wrote:
>>
>> On 19.11.21 15:06, Jan Beulich wrote:
>>> On 19.11.2021 13:50, Oleksandr Andrushchenko wrote:
>>>> On 19.11.21 14:45, Jan Beulich wrote:
>>>>> On 19.11.2021 13:13, Oleksandr Andrushchenko wrote:
>>>>>> On 19.11.21 14:05, Jan Beulich wrote:
>>>>>>> On 05.11.2021 07:56, Oleksandr Andrushchenko wrote:
>>>>>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
>>>>>>>>
>>>>>>>> Instead of handling a single range set, that contains all the memory
>>>>>>>> regions of all the BARs and ROM, have them per BAR.
>>>>>>> Iirc Roger did indicate agreement with the spitting. May I nevertheless
>>>>>>> ask that for posterity you say a word here about the overhead, to make
>>>>>>> clear this was a conscious decision?
>>>>>> Sure, but could you please help me with that sentence to please your
>>>>>> eye? I mean that it was you seeing the overhead while I was not as
>>>>>> to implement the similar functionality as range sets do I still think 
>>>>>> we'll
>>>>>> duplicate range sets at the end of the day.
>>>>> "Note that rangesets were chosen here despite there being only up to
>>>>> <N> separate ranges in each set (typically just 1)." Albeit that's
>>>>> then still lacking a justification for the choice. Ease of
>>>>> implementation?
>>>> I guess yes. I'll put:
>>>>
>>>> "Note that rangesets were chosen here despite there being only up to
>>>> <N> separate ranges in each set (typically just 1). But rangeset per BAR
>>>> was chosen for the ease of implementation and existing code re-usability."
>>> FTAOD please don't forget to replace the <N> - I wasn't sure if it would
>>> be 2 or 3.
>> It seems we can't put the exact number as it depends on how many MSI/MSI-X
>> holes are there and that depends on an arbitrary device properties.
> There aren't any MSI holes, and there can be at most 2 MSI-X holes iirc
> (MSI-X table and PBA). What I don't recall is whether there are
> constraints on these two, but istr them being fully independent. This
> would make the upper bound 3 (both in one BAR, other BARs then all using
> just a single range).
So if they are both in a single BAR (this is what I probably saw while
running QEMU for PVH Dom0 tests), then we may have up to 3 range
sets per BAR at max, so I will use 3 instead of N in description and will
probably put some description how we came up with N == 3.
>
> Jan
>
Thank you!!
Oleksandr