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

Yury Norov
2022-12-08T20:51:52Z

On Thu, Dec 08, 2022 at 10:22:22PM +0200, Tariq Toukan wrote:
>
>
> On 12/8/2022 8:30 PM, 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@nvidia.com/
> >
> > 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@gmail.com/T/
> > v2: https://lore.kernel.org/all/20221112190946.728270-3-yury.norov@gmail.com/T/
> > v3:
> > - fix typo in find_nth_and_andnot_bit();
> > - add 5th patch that simplifies cpumask_local_spread();
> > - address various coding style nits.
> >
> > Yury Norov (5):
> > lib/find: introduce find_nth_and_andnot_bit
> > cpumask: introduce cpumask_nth_and_andnot
> > sched: add sched_numa_find_nth_cpu()
> > cpumask: improve on cpumask_local_spread() locality
> > lib/cpumask: reorganize cpumask_local_spread() logic
> >
> > include/linux/cpumask.h | 20 ++++++++++++++
> > include/linux/find.h | 33 +++++++++++++++++++++++
> > include/linux/topology.h | 8 ++++++
> > kernel/sched/topology.c | 57 ++++++++++++++++++++++++++++++++++++++++
> > lib/cpumask.c | 26 +++++-------------
> > lib/find_bit.c | 9 +++++++
> > 6 files changed, 134 insertions(+), 19 deletions(-)
> >
>
> Acked-by: Tariq Toukan <tariqt@nvidia.com>

Thanks Tariq, Jacob and Peter for review. I'll add the series in
bitmap-for-next for testing. Still, I think that sched/numa branches
would be more suitable.

Thanks,
Yury