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

Andrew Morton
2008-08-14T16:34:34Z

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?

+ 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.

I give up. Have a little think about the stack bloat, please.

btw, whoever wrote that function is in need of a tab key.