[dpdk-dev] [RFC] mempool: add non-IO flag

[Ajit Khaparde]

On Wed, Aug 25, 2021 at 1:01 AM Thomas Monjalon <thomas at monjalon.net> wrote:
>
> +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.
+1

> >
> > 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.
+1

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