Scopes for P and E cores on hybrid chips (e.g. Alder Lake)

[andreapiacentini]

As a summary of a mail exchange:

On 13/02/2024 10:08, Andrea Piacentini wrote:

Hi Sam.
You can see, for instance, the hwloc documentation chapter on "Topology Attributes: Distances, Memory Attributes and CPU Kinds
":
https://www.open-mpi.org/projects/hwloc/doc/v2.8.0/a00366.php
It states that not all the linux flavours provide efficiency information and therefore in some cases the information comes from heuristics.

Strictly speaking the efficiency does not define a topological level, rather an attribute of some elements at the same level.
Yet I can easily think of an application targeting the computational tasks on the P cores subset and some service tasks (I/O, whatever) to the E cores.

By which syntax and which underlying implementation could Quo or Quo-Vadis help this targeting ?

Cheers
Andrea

On 13/02/2024 18:07, Gutierrez, Samuel K. wrote:

Hi Andrea,

Thank you.

I would have to think about this some more. That said, Quo probably can't right now. Quo-Vadis could by way of our use of hints, but it currently doesn't. If you're interested, please open an issue on the Quo-Vadis side so we don't lose track of this.

Thank you,

Sam

On 14/02/2024 03:12, Leon Borja, Edgar wrote:

Greetings, Andrea,

Adding to Sam’s response, Quo Vadis could support this use case via the ‘hint’ parameter of the ‘qv_scope_create’ call. The hints could look like:
QV_SCOPE_CREATE_E_CORE
QV_SCOPE_CREATE_P_CORE

For example:
qv_scope_create(ctx, input_scope, QV_HW_OBJ_CORE, ncores, QV_SCOPE_CREATE_E_CORE, &output_scope);

Hwloc would need to add the appropriate attributes to the cores, so that QV knows which cores are energy-efficiency-driven vs. performance-driven.

As Sam mentioned, if you add a GitHub issue, we will not forget :)

Thanks for bringing this up!
Edgar

[samuelkgutierrez]

I'm writing down a half-baked idea as a note to myself, so I don't forget:

Consider implementing a split that uses filter predicates for defining a scope. I can see this as helpful in this case since we can filter based on core type to segregate the P and E cores. I see other uses for this as well. This has the same spirit as a hint parameter, as suggested above. The trick is providing an expressive filtering system here.