Re: [PATCH 7/7] x86/resctrl: Determine if Sub-NUMA Cluster is enabled and initialize.

[Peter Newman]

Hi Tony,

On Fri, Mar 10, 2023 at 6:30 PM Tony Luck <tony.luck@xxxxxxxxx> wrote:
> Tell me more about your CPU-less nodes. Your fix avoids a bad
> pointer reference (because cpumask_first() returns cpu >= nr_cpu_ids
> for an empty bitmask).
>
> But now I'm worried about whether I have the right values in the
> formula:
>
> nr_node_ids / bitmap_weight(node_caches, nr_node_ids);
>
> This fix avoids counting the L3 from a non-existent CPU, but still
> counts the node in the numerator.
>
> Is your CPU-less node a full (non-SNC) node? Like this:
>
> Socket 0 Socket 1
> +--------------------+ +--------------------+
> | . | | . |
> | SNC 0.0 . SNC 0.1 | | zero . zero |
> | . | | CPUs . CPUs |
> | . | | . |
> | . | | . |
> +--------------------+ +--------------------+
> | L3 Cache | | L3 Cache |
> +--------------------+ +--------------------+

In the case I saw, the nodes were AEP DIMMs, so all-memory nodes.

Browsing sysfs, they are listed in has_memory, but not
has_normal_memory or has_cpu.

I imagine CXL.mem would have similar issues.

-Peter