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

Yury Norov
2023-04-20T05:19:55Z

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/20230216145455.661709-1-pawel.chmielewski@intel.com/

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(-)

--
2.34.1