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

[Jan Beulich <jbeulich@xxxxxxxx>]

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).

Jan