[dpdk-dev] [PATCH v3] doc: add stack mempool guide

[Eads, Gage]

Hi Olivier,

<snip>

> > +Stack Mempool Driver
> > +====================
> > +
> > +**rte_mempool_stack** is a pure software mempool driver based on the
> > +``rte_stack`` DPDK library. A stack-based mempool is often better suited to
> > +packet-processing workloads than a ring-based mempool, since its LIFO
> behavior
> > +results in better temporal locality and a minimal memory footprint even if the
> > +mempool is over-provisioned.
> 
> Would it make sense to give an example of a use-case where the stack
> driver should be used in place of the standard ring-based one?
> 
> In most run-to-completion applications, the mbufs stay in per-core
> caches, so changing the mempool driver won't have a big impact. However,
> I suspect that for applications using a pipeline model (ex: rx on core0,
> tx on core1), the stack model would be more efficient. Is it something
> that you measured? If yes, it would be useful to explain this in the
> documentation.
> 

Good point, I was overlooking the impact of the per-core caches. I've seen data showing
better overall packet throughput with the stack mempool, and indeed that was a pipelined
application. How about this re-write?

"
**rte_mempool_stack** is a pure software mempool driver based on the
``rte_stack`` DPDK library. For run-to-completion workloads with sufficiently
large per-lcore caches, the mbufs will likely stay in the per-lcore caches and the
mempool type (ring, stack, etc.) will have a negligible impact on performance. However
a stack-based mempool is often better suited to pipelined packet-processing workloads
(which allocate and free mbufs on different lcores) than a ring-based mempool, since its
LIFO behavior results in better temporal locality and a minimal memory footprint even
if the mempool is over-provisioned. Users are encouraged to benchmark with multiple
mempool types to determine which works best for their specific application.
"

Thanks,
Gage