Re: [RFC PATCH] sparse_irq aka dyn_irq

[Yinghai Lu]

On Sat, Nov 8, 2008 at 11:38 PM, Ingo Molnar <mingo@xxxxxxx> wrote:
>
> General impression: very nice patch!
>
> A lot of the structural problems have been addressed: the descriptor
> lookup is now hashed, the dynarray stuff got cleaned up / eliminated,
> the irq_desc->chip_data binding is very nice as well.
>
> (And the patch needs to be split up like it was in the past, once all
> review feedback has been seen and addressed.)
>
>> +config HAVE_SPARSE_IRQ
>> +     bool
>> +     default y
>
> i think it should be made user-configurable - at least initially. It
> should not cause extra complications, right?

io_apic.c will get more complicated.

>
>> +     if (irq < NR_IRQS_LEGACY) {
>
> please s/NR_IRQS_LEGACY/NR_IRQS_X86_LEGACY - this is never used
> outside of x86 code.

will use that in kernel/irq/handle.c too, because dyn_array is dumped.

>
>> +             cfg_new = desc_new->chip_data;
>
> the chip_data binding is a nice touch.
>
>> -     irq_want = build_irq_for_pci_dev(dev) + 0x100;
>> +     irq_want = build_irq_for_pci_dev(dev) + 0xfff;
>
> please replace magic constant with a properly named constant.
>
>> -     if (WARN_ON(nr > NR_IRQS))
>> -             nr = NR_IRQS;
>
> this will have to stay for the !SPARSE_IRQ case.

Yes

>
>> +++ linux-2.6/arch/x86/mm/init_32.c
>> @@ -66,6 +66,7 @@ static unsigned long __meminitdata table
>>  static unsigned long __meminitdata table_top;
>>
>>  static int __initdata after_init_bootmem;
>> +int after_bootmem;
>>
>>  static __init void *alloc_low_page(unsigned long *phys)
>>  {
>> @@ -987,6 +988,8 @@ void __init mem_init(void)
>>
>>       set_highmem_pages_init();
>>
>> +     after_bootmem = 1;
>
> this hack can go away once we have a proper percpu_alloc() that can be
> used early enough.

where is that fancy patch?
current percpu_alloc(), will keep big pointer in array..., instead of
put that pointer in percpu_area

64bit has that after_bootmem already.

>
>> +#ifndef CONFIG_HAVE_SPARSE_IRQ
>
> i'd suggest s/HAVE_SPARSE_IRQ/SPARSE_IRQ - as the HAVE_* flags are for
> architecture code to signal the presence of a facility.

OK

>
>> +#ifndef CONFIG_HAVE_SPARSE_IRQ
>>       if (irq >= nr_irqs)
>>               return;
>> +#endif
>
> we should hide as many ugly #ifdefs as possible, and define nr_irqs to
> NR_IRQS in the !SPARSE_IRQ case.
>
>> +++ linux-2.6/drivers/pci/htirq.c
>> @@ -82,6 +82,18 @@ void unmask_ht_irq(unsigned int irq)
>>       write_ht_irq_msg(irq, &msg);
>>  }
>>
>> +static unsigned int build_irq_for_pci_dev(struct pci_dev *dev)
>> +{
>> +     unsigned int irq;
>> +
>> +     irq = dev->bus->number;
>> +     irq <<= 8;
>> +     irq |= dev->devfn;
>> +     irq <<= 12;
>> +
>> +     return irq;
>
> magic constants should be named.

should add more comment here.

>
>> +#ifdef CONFIG_HAVE_SPARSE_IRQ
>> +     irq = create_irq_nr(irq_want + idx);
>> +#else
>>       irq = create_irq();
>> +#endif
>
> please eliminate this #ifdef by adding one new API:
> create_irq_nr(idx), which just maps to the create_irq() API in the
> !SPARSE_IRQ case.
>
>>  static struct irq_2_iommu *irq_2_iommu(unsigned int irq)
>>  {
>> -     return (irq < nr_irqs) ? irq_2_iommuX + irq : NULL;
>> +     struct irq_desc *desc;
>> +
>> +     desc = irq_to_desc(irq);
>> +
>> +     BUG_ON(!desc);
>> +
>> +     return desc->irq_2_iommu;
>
> the BUG_ON() is not too friendly, please do something like this
> instead:
>
>        if (WARN_ON_ONCE(!desc))
>                return NULL;
>
>> +#ifndef CONFIG_HAVE_SPARSE_IRQ
>>       /* protect irq_2_iommu_alloc later */
>>       if (irq >= nr_irqs)
>>               return -1;
>> +#endif
>
> this #ifdef can be eliminated too and turned into straight code via
> the #define nr_irqs NR_IRQS trick in the !SPARSE_IRQ case.
>
>> -     for_each_irq_desc(i, desc)
>> +     for_each_irq_desc(i, desc) {
>>               desc->affinity = cpumask_of_cpu(0);
>> +     } end_for_each_irq_desc();
>
> Sidenote: later on, once the patch is upstream, we should do a global
> rename:
>
>  s/for_each_irq_desc/do_each_irq_desc
>  s/end_for_each_irq_desc/while_each_irq_desc
>
> as it's much harder to miss the "while" in a "do ..." loop, than it is
> to miss the "end" in a "for" loop.
>
>> +#ifdef CONFIG_HAVE_SPARSE_IRQ
>> +static struct irq_desc irq_desc_init = {
>> +     .irq = -1U,
>> +     .status = IRQ_DISABLED,
>> +     .chip = &no_irq_chip,
>> +     .handle_irq = handle_bad_irq,
>> +     .depth = 1,
>> +     .lock = __SPIN_LOCK_UNLOCKED(irq_desc_init.lock),
>> +#ifdef CONFIG_SMP
>> +     .affinity = CPU_MASK_ALL
>> +#endif
>> +};
>
> please align structure fields vertically.
>
>> +static struct irq_desc irq_desc_legacy[NR_IRQS_LEGACY] __cacheline_aligned_in_smp = {
>> +     [0 ... NR_IRQS_LEGACY-1] = {
>> +             .irq = -1U,
>> +             .status = IRQ_DISABLED,
>> +             .chip = &no_irq_chip,
>> +             .handle_irq = handle_bad_irq,
>> +             .depth = 1,
>> +             .lock = __SPIN_LOCK_UNLOCKED(irq_desc_init.lock),
>> +#ifdef CONFIG_SMP
>> +             .affinity = CPU_MASK_ALL
>> +#endif
>> +     }
>> +};
>
> same here.
>
>> @@ -199,7 +200,6 @@ extern void reinit_intr_remapped_IO_APIC
>>  #endif
>>
>>  extern int probe_nr_irqs(void);
>> -
>>  #else  /* !CONFIG_X86_IO_APIC */
>>  #define io_apic_assign_pci_irqs 0
>>  static const int timer_through_8259 = 0;
>
> that's a spurious removal of a newline.

.....

YH
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