Re: [PATCH 3/4] irq: initialize nr_irqs based on nr_cpu_ids

Mike Travis
2009-01-11T02:00:40Z

Ingo Molnar wrote:
> * Mike Travis <travis@sgi.com> wrote:
>
>> Impact: Reduce memory usage.
>>
>> This is the second half of the changes to make the irq_desc_ptrs be
>> variable sized based on nr_cpu_ids. The algorithm is the same as the
>> setting of NR_IRQS except use nr_cpu_ids instead of NR_CPUS. This is
>> only when CONFIG_SPARSE_IRQS=y.
>>
>> Signed-off-by: Mike Travis <travis@sgi.com>
>> ---
>> kernel/irq/handle.c | 5 +++++
>> 1 file changed, 5 insertions(+)
>>
>> Files linux-2.6-for-ingo.orig/kernel/irq/.handle.c.swp and linux-2.6-for-ingo/kernel/irq/.handle.c.swp differ
>> --- linux-2.6-for-ingo.orig/kernel/irq/handle.c
>> +++ linux-2.6-for-ingo/kernel/irq/handle.c
>> @@ -133,6 +133,11 @@ int __init early_irq_init(void)
>> int legacy_count;
>> int i;
>>
>> + /* initialize nr_irqs based on nr_cpu_ids */
>> + nr_irqs = (8 * nr_cpu_ids) > (32 * MAX_IO_APICS) ?
>> + NR_VECTORS + (8 * nr_cpu_ids) :
>> + NR_VECTORS + (32 * MAX_IO_APICS);
>> +
>
> this will break non-x86. Please move this to the x86 early-irq-init
> function instead, and also sync it up with the current NR_IRQS sizing
> macro.
>
> I.e. do not duplicate the numbers but introduce some sort of
> max_nr_irqs(nr_cpus) define that is used to initialize NR_IRQS and also
> used later on to narrow down nr_irqs later on.

The way it is laid out is:

kernel/softirq.c:

int __init __weak early_irq_init(void)
{
return 0;
}

kernel/irq/handle.c:

#ifdef CONFIG_SPARSE_IRQ
:
struct irq_desc **irq_desc_ptrs __read_mostly;
:
int __init early_irq_init(void)
{
:
nr_irqs = ...

#else
:
struct irq_desc irq_desc[NR_IRQS] __cacheline_aligned_in_smp = {
:
int __init early_irq_init(void)
{
<don't set nr_irqs>

So I don't see an x86 specific early_irq_init.

Since NR_IRQS is defined in a lot of different ways (in different places),
I think I'll have to do something like;

arch/x86/include/asm/irq_vectors.h:

#define max_nr_irqs(nr_cpus) \

include/linux/irqnr.h:

#ifndef max_nr_irqs
#define max_nr_irqs(unused) NR_IRQS
#endif

Would that work for you?

Thanks,
Mike