From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH] If interrupt injection is not possible do not scan IRR.
Date: Mon, 18 May 2009 12:08:06 +0300
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To: Avi Kivity <avi@redhat.com>
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On Mon, May 18, 2009 at 12:00:40PM +0300, Avi Kivity wrote:
> Gleb Natapov wrote:
>> @@ -3174,10 +3174,11 @@ static void inject_pending_irq(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>>  			vcpu->arch.nmi_injected = true;
>>  			kvm_x86_ops->set_nmi(vcpu);
>>  		}
>> -	} else if (kvm_cpu_has_interrupt(vcpu)) {
>> -		if (kvm_x86_ops->interrupt_allowed(vcpu)) {
>> -			kvm_queue_interrupt(vcpu, kvm_cpu_get_interrupt(vcpu),
>> -					    false);
>> +	} else if (kvm_x86_ops->interrupt_allowed(vcpu)) {
>> +		int vec = kvm_cpu_get_interrupt(vcpu);
>> +		if (vec != -1) {
>> +			printk(KERN_ERR"inject %d rip=%x\n", vec, kvm_rip_read(vcpu));
>> +			kvm_queue_interrupt(vcpu, vec, false);
>>  			kvm_x86_ops->set_irq(vcpu);
>>  		} 	}
>>   
>
> Not sure if this is a win.  Usually interrupts are allowed, so we'll  
> have to do both calculations.  On vmx ->interrupt_allowed() reads the  
> vmcs, which is slow.
>
Depend on how slow vmcs read is. In case when interrupt is available we
also scan IRR twice with current code: first time in kvm_cpu_has_interrupt()
and another in kvm_cpu_get_interrupt().

If we want to optimize vmcs access, and for nested virtualization we may
want to do it, we can read common ones on exit and use in memory copy.

--
			Gleb.