Re: [dpdk-dev] [PATCH] parray: introduce internal API for dynamic arrays

["Morten Brørup" <mb@smartsharesystems.com>]

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas Monjalon
> Sent: Tuesday, 15 June 2021 08.48
> 
> 14/06/2021 17:48, Morten Brørup:
> > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas
> Monjalon
> > It would be much simpler to just increase RTE_MAX_ETHPORTS to
> something big enough to hold a sufficiently large array. And possibly
> add an rte_max_ethports variable to indicate the number of populated
> entries in the array, for use when iterating over the array.
> >
> > Can we come up with another example than RTE_MAX_ETHPORTS where this
> library provides a better benefit?
> 
> What is big enough?
> Is 640KB enough for RAM? ;)

Good point!

I think we agree that:
- The cost of this library is some added complexity, i.e. working with a dynamically sized array through a library instead of just indexing into a compile time fixed size array.
- The main benefit of this library is saving some RAM (and still allowing a potentially very high number of ports.)

My point was: The amount of RAM we are saving is a key parameter for the cost/benefit analysis. And since I don't think the rte_eth_devices[] array uses a significant amount of memory, I was asking for some other array using more memory, where the cost/benefit analysis would come out more advantageous to your proposed parray library.

> 
> When dealing with microservices switching, the numbers can increase
> very fast.

Yes, I strongly supported increasing the port_id type from 8 to 16 bits for this reason, when it was discussed at the DPDK Userspace a few years ago in Dublin. And with large RTE_MAX_QUEUES_PER_PORT values, the rte_eth_dev structure uses quite a lot of space for the rx/tx callback arrays. But the memory usage of rte_eth_devices[] is still relatively insignificant in a system wide context.

If main purpose is to optimize the rte_eth_devices[] array, I think there are better alternatives than this library. Bruce and Konstantin already threw a few ideas on the table.