On 06/08/2017 01:05 PM, Santosh Shukla wrote:
Q) Why do we need such infrastructure? A) Some NPU hardware like OCTEONTX follows push model to get the packet from the pktio device. Where packet allocation and freeing done by the HW. Since HW can operate only on IOVA with help of SMMU/IOMMU, when packet receives from the Ethernet device, it is the IOVA address (which is PA in existing scheme). Mapping IOVA as PA is expensive on those HW, where every packet needs to be converted to VA from PA/IOVA. This patchset proposes the method to autodetect the preferred IOVA mode for a device. Summary of IOVA scheme: - If all the devices are iommu capable and support IOMMU capable driver then selects IOVA_VA. - If any of the devices are non-iommu then use default IOVA scheme ie. IOVA_PA. - If no device found then IOVA scheme would be IOVA_DC (Don't care).
Isn't it possible to have a per-device granularity? For example, with virt case, having a physical NIC using VFIO with iommu, and virtio devices with noiommu. If the physical NIC prefers working with VAs, why forcing it to use PAs? Maybe I missed a limitation though. Cheers, Maxime
