Query: Boot time allocation of irq descriptors

Query: Boot time allocation of irq descriptors

[Vijay Kilari]

Hi ,

  I just glaced at the x86 code, here nr_irqs are set to 1024, which includes
normal irq's and MSI's. Memory for these descriptors are allocated at boot time.
is it correct?

int __init init_irq_data(void)
{

...
    for (vector = 0; vector < NR_VECTORS; ++vector)
        this_cpu(vector_irq)[vector] = INT_MIN;

    irq_desc = xzalloc_array(struct irq_desc, nr_irqs);

...
}


In xen/include/asm-x86/irq.h

#define MSI_IRQ(irq)       ((irq) >= nr_irqs_gsi && (irq) < nr_irqs)


Regards
Vijay

Re: Query: Boot time allocation of irq descriptors

[Andrew Cooper]

On 11/02/15 14:50, Vijay Kilari wrote:
> Hi ,
>
>   I just glaced at the x86 code, here nr_irqs are set to 1024, which includes
> normal irq's and MSI's. Memory for these descriptors are allocated at boot time.
> is it correct?
>
> int __init init_irq_data(void)
> {
>
> ...
>     for (vector = 0; vector < NR_VECTORS; ++vector)
>         this_cpu(vector_irq)[vector] = INT_MIN;
>
>     irq_desc = xzalloc_array(struct irq_desc, nr_irqs);
>
> ...
> }
>
>
> In xen/include/asm-x86/irq.h
>
> #define MSI_IRQ(irq)       ((irq) >= nr_irqs_gsi && (irq) < nr_irqs)

What do you think is incorrect about it?

~Andrew

Re: Query: Boot time allocation of irq descriptors

[Vijay Kilari]

On Wed, Feb 11, 2015 at 8:25 PM, Andrew Cooper
<andrew.cooper3@citrix.com> wrote:
> On 11/02/15 14:50, Vijay Kilari wrote:
>> Hi ,
>>
>>   I just glaced at the x86 code, here nr_irqs are set to 1024, which includes
>> normal irq's and MSI's. Memory for these descriptors are allocated at boot time.
>> is it correct?
>>
>> int __init init_irq_data(void)
>> {
>>
>> ...
>>     for (vector = 0; vector < NR_VECTORS; ++vector)
>>         this_cpu(vector_irq)[vector] = INT_MIN;
>>
>>     irq_desc = xzalloc_array(struct irq_desc, nr_irqs);
>>
>> ...
>> }
>>
>>
>> In xen/include/asm-x86/irq.h
>>
>> #define MSI_IRQ(irq)       ((irq) >= nr_irqs_gsi && (irq) < nr_irqs)
>
> What do you think is incorrect about it?

Nothing wrong with it.

  I am trying to add MSI support for arm64 where the number of
MSI interrupts are not limited to 1024. It can support large number of MSI's.
Just trying to understand how many MSI's that x86 supports and is there
any generic code that I can use for arm64.

Looks like I have to do something for arm64

Re: Query: Boot time allocation of irq descriptors

[Jan Beulich]

>>> On 11.02.15 at 16:03, <vijay.kilari@gmail.com> wrote:
> On Wed, Feb 11, 2015 at 8:25 PM, Andrew Cooper
> <andrew.cooper3@citrix.com> wrote:
>> On 11/02/15 14:50, Vijay Kilari wrote:
>>> Hi ,
>>>
>>>   I just glaced at the x86 code, here nr_irqs are set to 1024, which 
> includes
>>> normal irq's and MSI's. Memory for these descriptors are allocated at boot 
> time.
>>> is it correct?
>>>
>>> int __init init_irq_data(void)
>>> {
>>>
>>> ...
>>>     for (vector = 0; vector < NR_VECTORS; ++vector)
>>>         this_cpu(vector_irq)[vector] = INT_MIN;
>>>
>>>     irq_desc = xzalloc_array(struct irq_desc, nr_irqs);
>>>
>>> ...
>>> }
>>>
>>>
>>> In xen/include/asm-x86/irq.h
>>>
>>> #define MSI_IRQ(irq)       ((irq) >= nr_irqs_gsi && (irq) < nr_irqs)
>>
>> What do you think is incorrect about it?
> 
> Nothing wrong with it.
> 
>   I am trying to add MSI support for arm64 where the number of
> MSI interrupts are not limited to 1024. It can support large number of 
> MSI's.

So where did you spot this 1024? What I find (and wrote) is

    if ( nr_irqs == 0 )
        nr_irqs = cpu_has_apic ?
                  max(16U + num_present_cpus() * NR_DYNAMIC_VECTORS,
                      8 * nr_irqs_gsi) :
                  nr_irqs_gsi;
    else if ( nr_irqs < 16 )
        nr_irqs = 16;

Jan

Re: Query: Boot time allocation of irq descriptors

[Jan Beulich]

>>> On 11.02.15 at 15:50, <vijay.kilari@gmail.com> wrote:
>   I just glaced at the x86 code, here nr_irqs are set to 1024, which 
> includes
> normal irq's and MSI's. Memory for these descriptors are allocated at boot 
> time.
> is it correct?
> 
> int __init init_irq_data(void)
> {
> 
> ...
>     for (vector = 0; vector < NR_VECTORS; ++vector)
>         this_cpu(vector_irq)[vector] = INT_MIN;
> 
>     irq_desc = xzalloc_array(struct irq_desc, nr_irqs);

One day we'd like to allocate at least the MSI ones only on demand...

Jan