Re: [PATCH v3 7/9] sched/topology: Introduce sched_numa_hop_mask()

[Valentin Schneider <vschneid@redhat.com>]

On 26/08/22 16:14, Yicong Yang wrote:
> On 2022/8/26 2:12, Valentin Schneider wrote:
>> Tariq has pointed out that drivers allocating IRQ vectors would benefit
>> from having smarter NUMA-awareness - cpumask_local_spread() only knows
>> about the local node and everything outside is in the same bucket.
>>
>> sched_domains_numa_masks is pretty much what we want to hand out (a cpumask
>> of CPUs reachable within a given distance budget), introduce
>> sched_numa_hop_mask() to export those cpumasks.
>>
>> Link: http://lore.kernel.org/r/20220728191203.4055-1-tariqt@nvidia.com
>> Signed-off-by: Valentin Schneider <vschneid@redhat.com>
>> ---
>>  include/linux/topology.h |  9 +++++++++
>>  kernel/sched/topology.c  | 28 ++++++++++++++++++++++++++++
>>  2 files changed, 37 insertions(+)
>>
>> diff --git a/include/linux/topology.h b/include/linux/topology.h
>> index 4564faafd0e1..13b82b83e547 100644
>> --- a/include/linux/topology.h
>> +++ b/include/linux/topology.h
>> @@ -245,5 +245,14 @@ static inline const struct cpumask *cpu_cpu_mask(int cpu)
>>      return cpumask_of_node(cpu_to_node(cpu));
>>  }
>>
>> +#ifdef CONFIG_NUMA
>> +extern const struct cpumask *sched_numa_hop_mask(int node, int hops);
>> +#else
>> +static inline const struct cpumask *sched_numa_hop_mask(int node, int hops)
>> +{
>> +	return ERR_PTR(-EOPNOTSUPP);
>> +}
>> +#endif	/* CONFIG_NUMA */
>> +
>>
>
> I think it should be better to return cpu_online_mask() if CONFIG_NUMA=n and hop is 0. Then we
> can keep the behaviour consistent with cpumask_local_spread() which for_each_numa_hop_cpu is
> going to replace.
>

That's a good point, thanks.

> The macro checking maybe unnecessary, check whether node is NUMA_NO_NODE will handle the case
> where NUMA is not configured.
>
> Thanks.