Re: [PATCH v4 4/5] spapr_numa: consider user input when defining associativity

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 10/7/20 7:28 PM, Daniel Henrique Barboza wrote:
> A new function called spapr_numa_define_associativity_domains()
> is created to calculate the associativity domains and change
> the associativity arrays considering user input. This is how
> the associativity domain between two NUMA nodes A and B is
> calculated:
> 
> - get the distance D between them
> 
> - get the correspondent NUMA level 'n_level' for D. This is done
> via a helper called spapr_numa_get_numa_level()
> 
> - all associativity arrays were initialized with their own
> numa_ids, and we're calculating the distance in node_id ascending
> order, starting from node id 0 (the first node retrieved by
> numa_state). This will have a cascade effect in the algorithm because
> the associativity domains that node 0 defines will be carried over to
> other nodes, and node 1 associativities will be carried over after
> taking node 0 associativities into account, and so on. This
> happens because we'll assign assoc_src as the associativity domain
> of dst as well, for all NUMA levels beyond and including n_level.
> 
> The PPC kernel expects the associativity domains of the first node
> (node id 0) to be always 0 [1], and this algorithm will grant that
> by default.
> 
> Ultimately, all of this results in a best effort approximation for
> the actual NUMA distances the user input in the command line. Given
> the nature of how PAPR itself interprets NUMA distances versus the
> expectations risen by how ACPI SLIT works, there might be better
> algorithms but, in the end, it'll also result in another way to
> approximate what the user really wanted.
> 
> To keep this commit message no longer than it already is, the next
> patch will update the existing documentation in ppc-spapr-numa.rst
> with more in depth details and design considerations/drawbacks.
> 
> [1] https://lore.kernel.org/linuxppc-dev/5e8fbea3-8faf-0951-172a-b41a2138fbcf@gmail.com/
> 
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> ---
>   capstone            |   2 +-
>   hw/ppc/spapr_numa.c | 110 +++++++++++++++++++++++++++++++++++++++++++-
>   2 files changed, 110 insertions(+), 2 deletions(-)
> 
> diff --git a/capstone b/capstone
> index f8b1b83301..22ead3e0bf 160000
> --- a/capstone
> +++ b/capstone
> @@ -1 +1 @@
> -Subproject commit f8b1b833015a4ae47110ed068e0deb7106ced66d
> +Subproject commit 22ead3e0bfdb87516656453336160e0a37b066bf

Certainly unrelated to your patch.