Re: [PATCH v2 8/8] KVM: Use eoi to track RTC interrupt delivery status

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Mar 18, 2013 at 03:24:39PM +0800, Yang Zhang wrote:
> From: Yang Zhang <yang.z.zhang@Intel.com>
> 
> Current interrupt coalescing logci which only used by RTC has conflict
> with Posted Interrupt.
> This patch introduces a new mechinism to use eoi to track interrupt:
> When delivering an interrupt to vcpu, the need_eoi set to number of
> vcpu that received the interrupt. And decrease it when each vcpu writing
> eoi. No subsequent RTC interrupt can deliver to vcpu until all vcpus
> write eoi.
> 
> Signed-off-by: Yang Zhang <yang.z.zhang@Intel.com>
> ---
>  virt/kvm/ioapic.c |   67 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 67 insertions(+), 0 deletions(-)
> 
> diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
> index 7e47da8..8d498e5 100644
> --- a/virt/kvm/ioapic.c
> +++ b/virt/kvm/ioapic.c
> @@ -130,6 +130,48 @@ static void rtc_irq_get_dest_vcpu(struct kvm_ioapic *ioapic, int irq)
>  	kvm_get_dest_vcpu(ioapic->kvm, &irqe, ioapic->rtc_status.vcpu_map);
>  }
>  
> +static void rtc_irq_set_eoi(struct kvm_ioapic *ioapic, int irq)
> +{
> +	union kvm_ioapic_redirect_entry *entry = &ioapic->redirtbl[irq];
> +
> +	if (irq != 8)
> +		return;
> +
> +	if (likely(!bitmap_empty(ioapic->rtc_status.vcpu_map, KVM_MAX_VCPUS))) {
> +		if (entry->fields.delivery_mode == APIC_DM_LOWEST)
> +			ioapic->rtc_status.need_eoi = 1;
> +		else {
> +			int weight;
> +			weight = bitmap_weight(ioapic->rtc_status.vcpu_map,
> +					sizeof(ioapic->rtc_status.vcpu_map));
> +			ioapic->rtc_status.need_eoi = weight;
> +		}
> +	}
> +}

Why two bitmaps are necessary? One should be enough.