Re: [PATCH v3 0/5] cpumask: improve on cpumask_local_spread() locality

[Jacob Keller]

On 12/8/2022 10:30 AM, Yury Norov wrote:
> cpumask_local_spread() currently checks local node for presence of i'th
> CPU, and then if it finds nothing makes a flat search among all non-local
> CPUs. We can do it better by checking CPUs per NUMA hops.
>
> This series is inspired by Tariq Toukan and Valentin Schneider's
> "net/mlx5e: Improve remote NUMA preferences used for the IRQ affinity
> hints"
>
> https://patchwork.kernel.org/project/netdevbpf/patch/20220728191203.4055-3-tariqt@xxxxxxxxxx/
>
> According to their measurements, for mlx5e:
>
>          Bottleneck in RX side is released, reached linerate (~1.8x speedup).
>          ~30% less cpu util on TX.
>
> This patch makes cpumask_local_spread() traversing CPUs based on NUMA
> distance, just as well, and I expect comparable improvement for its
> users, as in case of mlx5e.
>
> I tested new behavior on my VM with the following NUMA configuration:
>
> root@debian:~# numactl -H
> available: 4 nodes (0-3)
> node 0 cpus: 0 1 2 3
> node 0 size: 3869 MB
> node 0 free: 3740 MB
> node 1 cpus: 4 5
> node 1 size: 1969 MB
> node 1 free: 1937 MB
> node 2 cpus: 6 7
> node 2 size: 1967 MB
> node 2 free: 1873 MB
> node 3 cpus: 8 9 10 11 12 13 14 15
> node 3 size: 7842 MB
> node 3 free: 7723 MB
> node distances:
> node   0   1   2   3
>    0:  10  50  30  70
>    1:  50  10  70  30
>    2:  30  70  10  50
>    3:  70  30  50  10
>
> And the cpumask_local_spread() for each node and offset traversing looks
> like this:
>
> node 0:   0   1   2   3   6   7   4   5   8   9  10  11  12  13  14  15
> node 1:   4   5   8   9  10  11  12  13  14  15   0   1   2   3   6   7
> node 2:   6   7   0   1   2   3   8   9  10  11  12  13  14  15   4   5
> node 3:   8   9  10  11  12  13  14  15   4   5   6   7   0   1   2   3
>
> v1: https://lore.kernel.org/lkml/20221111040027.621646-5-yury.norov@xxxxxxxxx/T/
> v2: https://lore.kernel.org/all/20221112190946.728270-3-yury.norov@xxxxxxxxx/T/
> v3:
>   - fix typo in find_nth_and_andnot_bit();
>   - add 5th patch that simplifies cpumask_local_spread();
>   - address various coding style nits.

The whole series look reasonable to me!

Reviewed-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>