[dpdk-dev] [EXT] Re: [PATCH] bus/pci: fix IOVA as VA mode selection

[Burakov, Anatoly]

On 09-Jul-19 4:04 PM, Thomas Monjalon wrote:
> 09/07/2019 16:37, Burakov, Anatoly:
>> My view would be to always run in IOVA as VA by default and only falling
>> back to IOVA as PA if there is a need to do that. Yet, it seems that
>> whenever i try to bring this up, the response (not necessarily from you,
>> so this is not directed at you specifically) seems to be that because of
>> hotplug, we have to start in the "safest" (from device support point of
>> view) mode - that is, in IOVA as PA. Seeing how, as you claim, some
>> devices require IOVA as VA, then IOVA as PA is no longer the "safe"
>> default that all devices will support. Perhaps we can use this
>> opportunity to finally make IOVA as VA the default :)
> 
> That's a good point Anatoly. We need to decide what is the safest default.
> 
> About the capabilities flags, please let's agree that we want
> to express 3 cases, so we need 2 flags.

We do agree on this.

> About the preference of a mode for a device, if a mode is really
> bad for a device, I suggest to not advertise it in capabilities.

Yes, agree with that as well.

> 
> In order to take a better decision, we need a summary of the
> decision algorithm per layer, involving kernel driver capabilities
> and memory capabilities.
> 

This needs to be documented very well, as this seems to be a source of 
great confusion for us all. If all was spelled out in the docs, we 
wouldn't need this long discussion to figure out that we actually agree :D

-- 
Thanks,
Anatoly