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

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Message-ID: <20120517080731.GZ32036@redhat.com>
Date:	Thu, 17 May 2012 11:07:31 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, x86@...nel.org,
	kvm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.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 10:57:33AM +0300, Avi Kivity wrote:
> On 05/17/2012 10:49 AM, Michael S. Tsirkin wrote:
> > 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?
> >
> 
> No, let's refactor this so it makes sense.  The {has|get}_interrupt
> split is the cause of the problem, I think.  We need a single function,
> with callbacks that are called when an event happens.  The callbacks can
> request an irq window exit, inject an interrupt, play with pveoi, or
> cause a #vmexit.
> 
Not sure what do you mean here. I kind of like the code we have now, but
this may be because I understand it :)

--
			Gleb.
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