linux-kernel - Re: [PATCHv4 3/5] kvm: host side for eoi optimization

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Date:	Thu, 17 May 2012 10:49:47 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Marcelo Tosatti <mtosatti@...hat.com>, x86@...nel.org,
	kvm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Avi Kivity <avi@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 3/5] kvm: host side for eoi optimization

On Thu, May 17, 2012 at 10:28:41AM +0300, Gleb Natapov wrote:
> On Wed, May 16, 2012 at 10:07:58PM +0300, Michael S. Tsirkin wrote:
> > > This code is reached from kvm_cpu_get_interrupt(), but this function will
> > > not be called in above scenario.
> > 
> > I think I see. So this shall fix it also makes code cleaner
> > (no -2 hack). Right? kvm_apic_has_interrupt is called correct?
> > 
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index b4f7013..5a38e34 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -1273,8 +1273,12 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
> >  	highest_irr = apic_find_highest_irr(apic);
> >  	if (highest_irr == -1)
> >  		return -1;
> > -	if (((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)))
> > -		return -2;
> > +	/* Detect interrupt nesting and disable EOI optimization */
> > +	if ((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI)) {
> > +		if (pv_eoi_enabled(vcpu))
> > +			pv_eoi_clr_pending(vcpu);
> > +		return -1;
> > +	}
> >  	return highest_irr;
> >  }
> >  
> I do not like it. kvm_apic_has_interrupt() does not suppose to mutate
> state.

OK, so let's rename it so it's clear it can mutate state?

> > @@ -1306,10 +1310,6 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
> >  	int vector = kvm_apic_has_interrupt(vcpu);
> >  	struct kvm_lapic *apic = vcpu->arch.apic;
> >  
> > -	/* Detect interrupt nesting and disable EOI optimization */
> > -	if (pv_eoi_enabled(vcpu) && vector == -2)
> > -		pv_eoi_clr_pending(vcpu);
> > -
> >  	if (vector < 0)
> >  		return -1;
> >  
> 
> --
> 			Gleb.
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