Re: [dpdk-dev] [PATCH v4 0/6] introduce DMA memory mapping for external memory

[Thomas Monjalon <thomas@monjalon.net>]

10/03/2019 09:27, Shahaf Shuler:
> The DPDK APIs expose 3 different modes to work with memory used for DMA:
> 
> 1. Use the DPDK owned memory (backed by the DPDK provided hugepages).
> This memory is allocated by the DPDK libraries, included in the DPDK
> memory system (memseg lists) and automatically DMA mapped by the DPDK
> layers.
> 
> 2. Use memory allocated by the user and register to the DPDK memory
> systems. Upon registration of memory, the DPDK layers will DMA map it
> to all needed devices. After registration, allocation of this memory
> will be done with rte_*malloc APIs.
> 
> 3. Use memory allocated by the user and not registered to the DPDK memory
> system. This is for users who wants to have tight control on this
> memory (e.g. avoid the rte_malloc header).
> The user should create a memory, register it through rte_extmem_register
> API, and call DMA map function in order to register such memory to
> the different devices.
> 
> The scope of the patch focus on #3 above.
> 
> Currently the only way to map external memory is through VFIO
> (rte_vfio_dma_map). While VFIO is common, there are other vendors
> which use different ways to map memory (e.g. Mellanox and NXP).
> 
> The work in this patch moves the DMA mapping to vendor agnostic APIs.
> Device level DMA map and unmap APIs were added. Implementation of those
> APIs was done currently only for PCI devices.
> 
> For PCI bus devices, the pci driver can expose its own map and unmap
> functions to be used for the mapping. In case the driver doesn't provide
> any, the memory will be mapped, if possible, to IOMMU through VFIO APIs.
> 
> Application usage with those APIs is quite simple:
> * allocate memory
> * call rte_extmem_register on the memory chunk.
> * take a device, and query its rte_device.
> * call the device specific mapping function for this device.
> 
> Future work will deprecate the rte_vfio_dma_map and rte_vfio_dma_unmap
> APIs, leaving the rte device APIs as the preferred option for the user.
> 
> Shahaf Shuler (6):
>   vfio: allow DMA map of memory for the default vfio fd
>   vfio: don't fail to DMA map if memory is already mapped
>   bus: introduce device level DMA memory mapping
>   net/mlx5: refactor external memory registration
>   net/mlx5: support PCI device DMA map and unmap
>   doc: deprecation notice for VFIO DMA map APIs

Applied, thanks