Re: [PATCH v2 7/8] lib: add test for for_each_numa_{cpu,hop_mask}()

Yury Norov
2023-04-26T05:51:26Z

Hi Valentin,

Thanks for review!

On Mon, Apr 24, 2023 at 06:09:52PM +0100, Valentin Schneider wrote:
> On 19/04/23 22:19, Yury Norov wrote:
> > + for (node = 0; node < sched_domains_numa_levels; node++) {
> > + unsigned int hop, c = 0;
> > +
> > + rcu_read_lock();
> > + for_each_numa_cpu(cpu, hop, node, cpu_online_mask)
> > + expect_eq_uint(cpumask_local_spread(c++, node), cpu);
> > + rcu_read_unlock();
> > + }
>
> I'm not fond of the export of sched_domains_numa_levels, especially
> considering it's just there for tests.
>
> Furthermore, is there any value is testing parity with
> cpumask_local_spread()?

I wanted to emphasize that new NUMA-aware functions are coherent with
each other, just like find_nth_bit() is coherent with find_next_bit().

But all that coherence looks important only in non-NUMA case, because
client code may depend on fact that next CPU is never less than current.
This doesn't hold for NUMA iterators anyways...

> Rather, shouldn't we check that using this API does
> yield CPUs of increasing NUMA distance?
>
> Something like
>
> for_each_node(node) {
> unsigned int prev_cpu, hop = 0;
>
> cpu = cpumask_first(cpumask_of_node(node));
> prev_cpu = cpu;
>
> rcu_read_lock();
>
> /* Assert distance is monotonically increasing */
> for_each_numa_cpu(cpu, hop, node, cpu_online_mask) {
> expect_ge_uint(cpu_to_node(cpu), cpu_to_node(prev_cpu));
> prev_cpu = cpu;
> }
>
> rcu_read_unlock();
> }

Your version of the test looks more straightforward. I need to think
for more, but it looks like I can take it in v3.

Thanks,
Yury