Re: KVM: Merge MSI handling to kvm_set_irq

[Sheng Yang <sheng@linux.intel.com>]

On Thursday 08 January 2009 21:54:41 Mike Day wrote:
> On 07/01/09 18:42 +0800, Sheng Yang wrote:
> > Using kvm_set_irq to handle all interrupt injection.
> >
> > Signed-off-by: Sheng Yang <sheng@linux.intel.com>
> > ---
> >
> > +static void gsi_dispatch(struct kvm *kvm, u32 gsi)
>
> ...
>
> > +		case IOAPIC_FIXED:
> > +			for (vcpu_id = 0; deliver_bitmask != 0; vcpu_id++) {
> > +				if (!(deliver_bitmask & (1 << vcpu_id)))
> > +					continue;
> > +				deliver_bitmask &= ~(1 << vcpu_id);
> > +				vcpu = ioapic->kvm->vcpus[vcpu_id];
> > +				if (vcpu)
> > +					kvm_apic_set_irq(vcpu, vector,
> > +							trig_mode);
> > +			}
> > +			break;
> > +		default:
> > +			break;
> > +		}
>
> In cases such as the for() loop above, which are numerous in the
> patchset, I wonder if using bitops would be slightly better:
>
> 		case IOAPIC_FIXED:
> 			while (deliver_bitmask != 0) {
> 				vcpu_id = ffs(deliver_bitmask);
> 				__clear_bit(vcpu_id - 1, &deliver_bitmask);
> 				vcpu = ioapic->kvm->vcpus[vcpu_id - 1];
> 				if (vcpu)
> 					kvm_apic_set_irq(vcpu, vector,
> 							 trig_mode);
> 			} ;
>
>
> I did a quick check and the second example compiles to a more
> consise set of assembler instructions. The current code uses bitops in
> cases like this.
>

Yes, that's what I did for bitmap changing in the following patches. Please 
refer to "[PATCH 10/10] KVM: bit ops for deliver_bitmap" I sent before.

-- 
regards
Yang, Sheng

> Mike