On 09/14/20 12:26, Valentin Schneider wrote:
>
> On 14/09/20 12:08, Qais Yousef wrote:
> > On 09/14/20 11:31, Valentin Schneider wrote:
> >>
> >> On 12/09/20 00:04, Li, Aubrey wrote:
> >> >>> +++ b/include/linux/sched/topology.h
> >> >>> @@ -65,8 +65,21 @@ struct sched_domain_shared {
> >> >>> atomic_t ref;
> >> >>> atomic_t nr_busy_cpus;
> >> >>> int has_idle_cores;
> >> >>> + /*
> >> >>> + * Span of all idle CPUs in this domain.
> >> >>> + *
> >> >>> + * NOTE: this field is variable length. (Allocated dynamically
> >> >>> + * by attaching extra space to the end of the structure,
> >> >>> + * depending on how many CPUs the kernel has booted up with)
> >> >>> + */
> >> >>> + unsigned long idle_cpus_span[];
> >> >>
> >> >> Can't you use cpumask_var_t and zalloc_cpumask_var() instead?
> >> >
> >> > I can use the existing free code. Do we have a problem of this?
> >> >
> >>
> >> Nah, flexible array members are the preferred approach here; this also
> >
> > Is this your opinion or a rule written somewhere I missed?
>
> I don't think there's a written rule, but AIUI it is preferred by at
> least Peter:
>
> https://lore.kernel.org/linux-pm/20180612125930.gp12...@hirez.programming.kicks-ass.net/
> https://lore.kernel.org/lkml/20180619110734.go2...@hirez.programming.kicks-ass.net/
>
> And my opinion is that, if you can, having fewer separate allocation is
> better.
+1
>
> >
> >> means we don't let CONFIG_CPUMASK_OFFSTACK dictate where this gets
> >> allocated.
> >>
> >> See struct numa_group, struct sched_group, struct sched_domain, struct
> >> em_perf_domain...
> >
> > struct root_domain, struct cpupri_vec, struct generic_pm_domain,
> > struct irq_common_data..
> >
> > Use cpumask_var_t.
> >
> > Both approach look correct to me, so no objection in principle.
> > cpumask_var_t
> > looks neater IMO and will be necessary once more than one cpumask are
> > required
> > in a struct.
> >
>
> You're right in that cpumask_var_t becomes necessary when you need more
> than one mask. For those that use it despite requiring only one mask
> (cpupri stuff, struct nohz too), I'm not sure.
I don't have a strong opinoin. cpumask_var_t is more readable and maintainble
IMO. But it's not a big deal. Any form can be easily changed.
Thanks
--
Qais Yousef
