Re: [PATCH] irq: sparse irqs, fix #2

Eric W. Biederman
2008-08-14T17:13:54Z

Andrew Morton <akpm@linux-foundation.org> writes:

> On Thu, 14 Aug 2008 15:36:52 +0200 Ingo Molnar <mingo@elte.hu> wrote:
>
>> +static inline cpumask_t vector_allocation_domain(int cpu)
>> +{
>> + /* Careful. Some cpus do not strictly honor the set of cpus
>> + * specified in the interrupt destination when using lowest
>> + * priority interrupt delivery mode.
>> + *
>> + * In particular there was a hyperthreading cpu observed to
>> + * deliver interrupts to the wrong hyperthread when only one
>> + * hyperthread was specified in the interrupt desitination.
>> + */
>> + cpumask_t domain = { { [0] = APIC_ALL_CPUS, } };
>> + return domain;
>> +}
>
> I haven't looked at callers of this, but...
>
> Does it need to be allocated on the stack? Local cpumask_t's are a
> size problem. Can we build this in .rodata at compile time instead?
>
> Is this the caller?

Yes.

>
> + for_each_cpu_mask(cpu, mask) {
> + cpumask_t domain, new_mask;
> + int new_cpu;
> + int vector;
> +
> + domain = vector_allocation_domain(cpu);
> + cpus_and(new_mask, domain, cpu_online_map);
>
> If so we could perhaps do
>
>
> static noinline const cpumask_t *vector_allocation_domain(int cpu)
> {
> /* Careful. Some cpus do not strictly honor the set of cpus
> * specified in the interrupt destination when using lowest
> * priority interrupt delivery mode.
> *
> * In particular there was a hyperthreading cpu observed to
> * deliver interrupts to the wrong hyperthread when only one
> * hyperthread was specified in the interrupt desitination.
> */
> static const cpumask_t domain = { { [0] = APIC_ALL_CPUS, } };
> return &domain;
> }
>
>
> ...
>
> + for_each_cpu_mask(cpu, mask) {
> + cpumask_t domain, new_mask;
> + int new_cpu;
> + int vector;
> +
> + __cpus_and(new_mask, vector_allocation_domain(cpu),
> + &cpu_online_map);
>
> otoh, perhaps this new function is one implementation of
> genapic.vector_allocation_domain(), in which case the inlining was
> unneeded and misleading.

Likely. Why these things live in header files...

> I give up. Have a little think about the stack bloat, please.
>
> btw, whoever wrote that function is in need of a tab key.

Unfortunate gradual accreation of functionality.

vector_allocation_domain could perhaps be better named. Round up
this cpu to the set of cpus I need to allocate a vector on.

Eric