Hi, On 12/11/22 11:09, 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 comparabale 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 > Is this meant as a replacement for [1]? I like that this is changing an existing interface so that all current users directly benefit from the change. Now, about half of the users of cpumask_local_spread() use it in a loop with incremental @i parameter, which makes the repeated bsearch a bit of a shame, but then I'm tempted to say the first point makes it worth it. [1]: https://lore.kernel.org/all/20221028164959.1367250-1-vschneid@xxxxxxxxxx/ > v1: https://lore.kernel.org/lkml/20221111040027.621646-5-yury.norov@xxxxxxxxx/T/ > v2: > - use bsearch() in sched_numa_find_nth_cpu(); > - fix missing 'static inline' in 3rd patch. > > Yury Norov (4): > 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 > > include/linux/cpumask.h | 20 +++++++++++++++ > include/linux/find.h | 33 ++++++++++++++++++++++++ > include/linux/topology.h | 8 ++++++ > kernel/sched/topology.c | 55 ++++++++++++++++++++++++++++++++++++++++ > lib/cpumask.c | 12 ++------- > lib/find_bit.c | 9 +++++++ > 6 files changed, 127 insertions(+), 10 deletions(-) > > -- > 2.34.1
