linux-kernel - Re: [PATCH] kvm: optimize ISR lookups

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Message-ID: <20120521215127.GH17031@redhat.com>
Date:	Tue, 22 May 2012 00:51:27 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	kvm@...r.kernel.org, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: optimize ISR lookups

On Mon, May 21, 2012 at 11:04:25PM +0200, Thomas Gleixner wrote:
> > @@ -242,6 +262,25 @@ static inline void apic_clear_irr(int vec, struct kvm_lapic *apic)
> >  		apic->irr_pending = true;
> >  }
> >  
> > +static inline void apic_set_isr(int vec, struct kvm_lapic *apic)
> > +{
> > +	if (!__apic_test_and_set_vector(vec, apic->regs + APIC_ISR))
> > +		++apic->isr_count;
> > +	ASSERT(apic->isr_count > MAX_APIC_VECTOR);
> 
> I'm really curious what you observed when defining DEBUG in that file.
> 
> Clearly you never did.

Sorry :(
Yes clearly silly, thanks for pointing this out.

> > +	if (likely(apic->isr_count == 1))
> > +		apic->isr_cache = vec;
> > +	else
> > +		apic->isr_cache = -1;
> > +}
> > +
> > +static inline void apic_clear_isr(int vec, struct kvm_lapic *apic)
> > +{
> > +	if (__apic_test_and_clear_vector(vec, apic->regs + APIC_ISR))
> > +		--apic->isr_count;
> > +	ASSERT(apic->isr_count < 0);
> 
> Ditto.
> 
> >  	result = find_highest_vector(apic->regs + APIC_ISR);
> >  	ASSERT(result == -1 || result >= 16);
> 
> And obviously none of the folks who added this gem bothered to define
> DEBUG either.
> 
> So please instead of working around horrid design decisions and adding
> more mess to the existing one, can we please cleanup the stuff first
> and then decide whether it's worth to add the extra magic?
> 
> Thanks,
> 
> 	tglx
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