RE: [Xen-devel] IRQ migration (c/s 20370 + 20465)

["Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>]

Hi, Jan
    I think the patch is fine. In directed eoi case, the 
io_apic_level_ack_pending check should be always true before eoi_IO_APIC_irq is 
called , so move_masked_irq is never called and  no IRQ migration occurs.  
Xiantao

Jan Beulich wrote:
>>>> On 29.11.10 at 14:14, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>>> Edwin, Xiantao, 
>> 
>> I'm observing I/O-APIC IRQs never getting migrated on a system
>> using directed EOI. Looking at end_level_ioapic_irq(), I fail
>> to see how that case is being handled (other than in the Linux
>> implementation, which this code supposedly is a clone of).
>> 
>> Additionally it seems wasteful to check whether to move the IRQ in
>> mask_and_ack_level_ioapic_irq(), as ack_APIC_irq() cannot
>> possibly have resulted in clearing any of the IRR bits that
>> io_apic_level_ack_pending() is looking at.
> 
> Below is a tentative (lightly tested) fix for this. Comments?
> 
> Jan
> 
> --- a/xen/arch/x86/io_apic.c
> +++ b/xen/arch/x86/io_apic.c
> @@ -1634,11 +1634,14 @@ static void mask_and_ack_level_ioapic_ir
> 
>      ack_APIC_irq();
> 
> +    if ( directed_eoi_enabled )
> +        return;
> +
>      if ((irq_desc[irq].status & IRQ_MOVE_PENDING) &&
>         !io_apic_level_ack_pending(irq))
> -        move_native_irq(irq);
> +        move_masked_irq(irq);
> 
> -    if (!directed_eoi_enabled && !(v & (1 << (i & 0x1f)))) {
> +    if ( !(v & (1 << (i & 0x1f))) ) {
>          atomic_inc(&irq_mis_count);
>          spin_lock(&ioapic_lock);
>          __edge_IO_APIC_irq(irq);
> @@ -1654,12 +1657,22 @@ static void end_level_ioapic_irq (unsign
> 
>      if ( !ioapic_ack_new )
>      {
> -        if ( irq_desc[irq].status & IRQ_DISABLED )
> -            return;
> -
>          if ( directed_eoi_enabled )
> +        {
> +            if ( !(irq_desc[irq].status &
> (IRQ_DISABLED|IRQ_MOVE_PENDING)) ) +            {
> +                eoi_IO_APIC_irq(irq);
> +                return;
> +            }
> +
> +            mask_IO_APIC_irq(irq);
>              eoi_IO_APIC_irq(irq);
> -        else
> +            if ( (irq_desc[irq].status & IRQ_MOVE_PENDING) &&
> +                 !io_apic_level_ack_pending(irq) )
> +                move_masked_irq(irq);
> +        }
> +
> +        if ( !(irq_desc[irq].status & IRQ_DISABLED) )
>              unmask_IO_APIC_irq(irq);
> 
>          return;


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