[dpdk-dev] [PATCH v4 2/4] eal: fix IOVA mode selection as VA for PCI drivers

[Ferruh Yigit]

On 11/25/2019 10:22 AM, Thomas Monjalon wrote:
> 25/11/2019 10:33, Ferruh Yigit:
>> It looks like DPDK application initialized as IOVA=VA,
>> and the new device is bound to 'igb_uio' which forces it to PA,
>> fails on above check.
> 
> Do you mean this use case was not tested earlier with DPDK 19.08?

Perhaps, just a guess, this can be side affect of only using LTS.

> 
> 
>> I would like to get your comment on the issue.
>>
>> For the OvS mode, hopefully binding the device to 'vfio-pci'
>> can be a solution, but for the cases we don't have that option,
>> can/should we force the DPDK to PA mode after initialization?
> 
> I think this is expected, because VA is the new default since 19.08:
> http://doc.dpdk.org/guides/rel_notes/release_19_08.html#new-features
> 
> In case, there is no constraint on initialization,
> we have to decide which mode is preferred.
> Previously PA was preferred.
> For the sake of modernity (and because it fits with some new devices),
> the preference has been changed to VA.
> 
> If igb_uio device is used at initialization,
> the PA mode should be used.
> If igb_uio (PA-only) device is hotplugged, no luck!
> If VA-only device is hotplugged, it works!
> 
> I think this change is one step in deprecating igb_uio.
> 

I just want to confirm/clarify that this behavior change is by design, not a defect.
Should we document this behavior change more clearly, or highlight more, to not 
let catch others too?