[v2,0/8] sched/topology: add for_each_numa_cpu() macro

Message

Yury Norov April 20, 2023, 5:19 a.m. UTC

for_each_cpu() is widely used in kernel, and it's beneficial to create
a NUMA-aware version of the macro.

Recently added for_each_numa_hop_mask() works, but switching existing
codebase to it is not an easy process.

This series adds for_each_numa_cpu(), which is designed to be similar to
the for_each_cpu(). It allows to convert existing code to NUMA-aware as
simple as adding a hop iterator variable and passing it inside new macro.
for_each_numa_cpu() takes care of the rest.

At the moment, we have 2 users of NUMA-aware enumerators. One is
Melanox's in-tree driver, and another is Intel's in-review driver:

https://lore.kernel.org/lkml/[e-mail]/

Both real-life examples follow the same pattern:

        for_each_numa_hop_mask(cpus, prev, node) {
                for_each_cpu_andnot(cpu, cpus, prev) {
                        if (cnt++ == max_num)
                                goto out;
                        do_something(cpu);
                }
                prev = cpus;
        }

With the new macro, it has a more standard look, like this:

        for_each_numa_cpu(cpu, hop, node, cpu_possible_mask) {
                if (cnt++ == max_num)
                        break;
                do_something(cpu);
        }

Straight conversion of existing for_each_cpu() codebase to NUMA-aware
version with for_each_numa_hop_mask() is difficult because it doesn't
take a user-provided cpu mask, and eventually ends up with open-coded
double loop. With for_each_numa_cpu() it shouldn't be a brainteaser.
Consider the NUMA-ignorant example:

        cpumask_t cpus = get_mask();
        int cnt = 0, cpu;

        for_each_cpu(cpu, cpus) {
                if (cnt++ == max_num)
                        break;
                do_something(cpu);
        }

Converting it to NUMA-aware version would be as simple as:

        cpumask_t cpus = get_mask();
        int node = get_node();
        int cnt = 0, hop, cpu;

        for_each_numa_cpu(cpu, hop, node, cpus) {
                if (cnt++ == max_num)
                        break;
                do_something(cpu);
        }

The latter looks more verbose and avoids from open-coding that annoying
double loop. Another advantage is that it works with a 'hop' parameter with
the clear meaning of NUMA distance, and doesn't make people not familiar
to enumerator internals bothering with current and previous masks machinery.

v2:
 - repase on top of master;
 - cleanup comments and tweak them to comply with kernel-doc;
 - remove RFC from patch #8 as there's no objections.

Yury Norov (8):
  lib/find: add find_next_and_andnot_bit()
  sched/topology: introduce sched_numa_find_next_cpu()
  sched/topology: add for_each_numa_cpu() macro
  net: mlx5: switch comp_irqs_request() to using for_each_numa_cpu
  lib/cpumask: update comment to cpumask_local_spread()
  sched/topology: export sched_domains_numa_levels
  lib: add test for for_each_numa_{cpu,hop_mask}()
  sched: drop for_each_numa_hop_mask()

 drivers/net/ethernet/mellanox/mlx5/core/eq.c | 16 ++----
 include/linux/find.h                         | 43 ++++++++++++++
 include/linux/topology.h                     | 37 ++++++------
 kernel/sched/topology.c                      | 59 +++++++++++---------
 lib/cpumask.c                                |  7 +--
 lib/find_bit.c                               | 12 ++++
 lib/test_bitmap.c                            | 16 ++++++
 7 files changed, 133 insertions(+), 57 deletions(-)