+1, I support this idea.
12/08/2021 14:43, Dmitry Kozlyuk:
> We propose to add a mempool flag MEMPOOL_F_NON_IO to mark pools of objects
> that
> will not be used with device IO and their memory for DMA. This will allow
> saving IOMMU entries by not mapping the memory used by such pools.
>
> Immediate use case is MLX5 PMD. The hardware has its internal IOMMU where PMD
> registers the memory. On the data path, PMD translates VA into a key consumed
> by the device IOMMU. It is impractical for the PMD to register all allocated
> memory because of increased lookup cost both in HW and SW. Most often mbuf
> memory comes from mempools, so if PMD tracked them, it could almost always
> have
> mbuf memory registered before an mbuf hits the PMD. The new flag would prevent
> the PMD for registering memory that will never need it. Tracking the mempools
> and dealing with them in MLX5 PMD is the next step after the proposed change.
>
> A possible use case is IOMMU management in EAL. Mempool could translate the
> new
> flag to a hint to the memory manager, which would use it to skip adding IOMMU
> entries in some cases.
>
> It was considered to add MEMPOOL_F_IO with the opposite meaning. It would be
> automatically set for pktmbuf pools; user would be able to set it for other
> pools. However, current assumption is that all DPDK memory is DMA-able,
> it is controversial to have a flag asserting this fact.
