RE: [PATCH v4 0/4] Introduce Topology NUMA grouping for lcores

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

> From: Varghese, Vipin [mailto:Vipin.Varghese@amd.com]
> Sent: Monday, 3 March 2025 10.06
> 
> [Public]
> 
> Hi Morten,
> 
> snipped
> 
> >
> > > From: Thomas Monjalon [mailto:thomas@monjalon.net]
> > > Sent: Thursday, 13 February 2025 09.34
> > >
> > > 13/02/2025 04:09, Varghese, Vipin:
> > > > [AMD Official Use Only - AMD Internal Distribution Only]
> > > >
> > > > Adding Thomas and Ajit to the loop.
> > > >
> > > > Hi Ajit, we have been using the patch series for identifying the
> > > topology and getting l3 cache id for populating the steering tag
> for
> > > Device Specific Model & MSI-x driven af-xdp for the experimental
> STAG
> > > firmware on Thor.
> >
> > Excellent. A real life example use case helps the review process a
> lot!
> 
> Steering tag is one of the examples or uses, as shared in the current
> patch series  we make use of these for other examples too.
> Eventdev, pkt-distributor and graph nodes are also in works to exploit
> L2|L3 cache local coherency too.
> 
> >
> > > >
> > > > Hence current use of topology library helps in 1. workload
> placement
> > > > in same Cache or IO domain 2. populating id for MSIx or Device
> > > > specific model for steering tags.
> > > >
> > > > Thomas and Ajith can we get some help to get this mainline too?
> > >
> > > Yes, sorry the review discussions did not start.
> > > It has been forgotten.
> >
> > I think the topology/domain API in the EAL should be co-designed with
> the steering
> > tag API in the ethdev library, so the design can be
> reviewed/discussed in its entirety.
> 
> As shared in the discussion, we have been exploring simplified approach
> for steering tags, namely
> 
> 1. pci-dev args (crude way)
> 2. flow api for RX (experimental way)
> 
> Based on the platform (in case of AMD EPYC, these are translated to `L3
> id + 1`)
> 
> We do agree rte_ethdev library can use topology API. Current topology
> API are designed to be made independent from steering tags, as other
> examples do make use of the same.
> 
> >
> > To help the review discussion, please consider describing the
> following:
> > Which APIs are for slow path, and which are for fast path?
> > Which APIs are "must have", i.e. core to making it work at all, and
> which APIs are
> > "nice to have", i.e. support APIs to ease use of the new features?
> 
> Yes, will try to do the same in updated version. For Slow and Fast path
> API I might need some help, as I was under the impression current
> behavior is same rte_lcore (invoked at setup and before remote launch).
> But will check again.

Probably they are all used for configuration only, and thus all slow path; but if there are any fast path APIs, they should be highlighted as such.

> 
> >
> > I haven't looked at the hwloc library's API; but I guess these new
> EAL functions are
> > closely related. Is it a thin wrapper around the hwloc library, or is
> it very different?
> This is very thin wrapper on top of hwloc library only. But with DPDK
> RTE_MAX_LCORE & RTE_NUMA boundary check and population.

OK. The hwloc library is portable across Linux, BSD and Windows, which is great!

Please also describe the benefits of using this DPDK library, compared to directly using the hwloc library.