[dpdk-dev] [RFC] mempool: implement index-based per core cache

[Morten Brørup]

> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Honnappa
> Nagarahalli
> Sent: Monday, 4 October 2021 18.36
> 
> <snip>
> >
> >
> > > > > Current mempool per core cache implementation is based on
> pointer
> > > > > For most architectures, each pointer consumes 64b Replace it
> with
> > > > > index-based implementation, where in each buffer is addressed
> by
> > > > > (pool address + index)

I like Dharmik's suggestion very much. CPU cache is a critical and limited resource.

DPDK has a tendency of using pointers where indexes could be used instead. I suppose pointers provide the additional flexibility of mixing entries from different memory pools, e.g. multiple mbuf pools.

> > > >
> > > > I don't think it is going to work:
> > > > On 64-bit systems difference between pool address and it's elem
> > > > address could be bigger than 4GB.
> > > Are you talking about a case where the memory pool size is more
> than 4GB?
> >
> > That is one possible scenario.

That could be solved by making the index an element index instead of a pointer offset: address = (pool address + index * element size).

> > Another possibility - user populates mempool himself with some
> external
> > memory by calling rte_mempool_populate_iova() directly.
> Is the concern that IOVA might not be contiguous for all the memory
> used by the mempool?
> 
> > I suppose such situation can even occur even with normal
> > rte_mempool_create(), though it should be a really rare one.
> All in all, this feature needs to be configurable during compile time.