[RFC] Fix cryptodev socket id for devices on unknown NUMA node

[Bruce Richardson]

On Tue, Jan 17, 2023 at 12:32:14PM +0100, Morten Brørup wrote:
> > From: Didier Pallard [mailto:didier.pallard at 6wind.com]
> > Sent: Tuesday, 17 January 2023 11.17
> > 
> > Since DPDK 22.11 and below commit:
> > https://git.dpdk.org/dpdk/commit/?id=7dcd73e37965ba0bfa430efeac362fe183
> > ed0ae2
> > rte_cryptodev_socket_id() could return an incorrect value of 255.
> > Problem has been seen during configuration of the qat device
> > on an Atom C3000 architecture. On this arch, PCI is not depending on
> > any numa socket, causing device numa_node to be equal to SOCKET_ID_ANY.
> 
> Disclaimer: I'm not up to speed with this topic or patch, so feel free to ignore my comments here! I'm only speaking up because I fear we are increasing the risk of bugs here. But again, please bear with me, if I have totally misunderstood this!
> 
> I was under the impression that single-socket systems used socket_id 0 as default. How can the PCI bus (or QAT device) not depend on any socket? It must be connected somewhere.
> 
> Doesn't assigning socket_id = -1 for devices (QAT or anything else) introduce a big risk of bugs, e.g. in comparisons? The special socket_id value -1 should have only two meanings: 1) return value "error", or 2) input value "any". Now it also can mean 3) "unknown"? How do comparison functions work for that... is "any" == "unknown"? And does searching for "0" match "unknown"? It might, or might not, but searching for "any" does match "0". And how about searching for "unknown", if such a value is propagate around in the system.
> 
> And if we started considering socket_id == -1 valid with that patch, should the return type of rte_socket_id(void) be signed instead of unsigned?
> 
The issue here is that not all PCI endpoints connect directly to a socket,
some connect to the chipset instead, and so do not have any numa affinity.
That was the original meaning of the "-1" value, and it came about from an
era before we had on-die PCI endpoints.

/Bruce