Re: [patch 2/5] KVM: reintroduce guest mode bit and unify remote request code

[Avi Kivity <avi@redhat.com>]

On 08/27/2009 04:20 AM, Marcelo Tosatti wrote:

> +}
> +
> +void kvm_vcpu_ipi(struct kvm_vcpu *vcpu)
> +{
> +	int me;
> +	int cpu = vcpu->cpu;
>
>   	me = get_cpu();
> -	if (cpu != me&&  (unsigned)cpu<  nr_cpu_ids&&  cpu_online(cpu))
> -		if (!test_and_set_bit(KVM_REQ_KICK,&vcpu->requests))
> -			smp_send_reschedule(cpu);
> +	if (cpu != me&&  (unsigned)cpu<  nr_cpu_ids&&  cpu_online(cpu)) {
> +		if (test_bit(KVM_VCPU_GUEST_MODE,&vcpu->vcpu_state)) {
> +			if (!test_and_set_bit(KVM_VCPU_KICKED,
> +					&vcpu->vcpu_state))
> +				smp_send_reschedule(cpu);
> +		}
> +	}
>   	put_cpu();
>   }
>
> @@ -168,6 +176,30 @@ static bool make_all_cpus_request(struct
>   	return called;
>   }
>
> +static int kvm_req_wait(void *unused)
> +{
> +	cpu_relax();
> +	return 0;
> +}
> +
> +static void kvm_vcpu_request(struct kvm_vcpu *vcpu, unsigned int req)
> +{
> +	set_bit(req,&vcpu->requests);
> +	barrier();
> +	kvm_vcpu_ipi(vcpu);
> +	wait_on_bit(&vcpu->vcpu_state, KVM_VCPU_GUEST_MODE, kvm_req_wait,
> +		    TASK_UNINTERRUPTIBLE);
> +}
> +
> +static void kvm_vcpus_request(struct kvm *kvm, unsigned int req)
> +{
> +	int i;
> +	struct kvm_vcpu *vcpu;
> +
> +	kvm_for_each_vcpu(i, vcpu, kvm)
> +		kvm_vcpu_request(vcpu, req);
> +}
>    

Gleb notes there are two problems here:  instead of using a multicast 
IPI, you're sending multiple unicast IPIs.  Second, you're serializing 
the waiting.  It would be better to batch-send the IPIs, then batch-wait 
for results.

-- 
error compiling committee.c: too many arguments to function