[dpdk-dev] [PATCH v10 3/9] linuxapp/eal_pci: get iommu class

[Tan, Jianfeng]

On 10/11/2017 12:43 PM, santosh wrote:
> On Wednesday 11 October 2017 07:17 AM, Tan, Jianfeng wrote:
>> Hi,
>>
>> Nice patch series. But I still have a small question about below flag.
>>
>>
>> On 10/6/2017 7:03 PM, Santosh Shukla wrote:
>>> Get iommu class of PCI device on the bus and returns preferred iova
>>> mapping mode for that bus.
>>>
>>> Patch also introduces RTE_PCI_DRV_IOVA_AS_VA drv flag.
>>> Flag used when driver needs to operate in iova=va mode.
>>>
>> Does this flag indicate a must to use VA as IOVA, or a nice-to-have one? In detail, above commit log says, "needs to operate in iova=va mode", but the comment in the patch indicates this flag means "driver supports IOVA as VA".
>>
>> If it's the latter case, I would suppose all drivers support to use VA as IOVA, if the NICs are binded to vfio-pci (iommu mode). Please correct me if I'm wrong.
>>
> - Any iommu backed pmd could choose to use this flag.

But if this is characterized by assumption for all PMDs, why do we 
trouble to introduce this flag.

> - Reasoning for need was performance for our external mempool pmd: avoid phy2virt translation on
> mbuf thus save cycles.
>

Agreed, and it's also for running DPDK without root privilege.

Thanks,
Jianfeng