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Date: Wed, 16 May 2012 20:48:19 +0300 From: Gleb Natapov <gleb@...hat.com> To: Marcelo Tosatti <mtosatti@...hat.com> Cc: "Michael S. Tsirkin" <mst@...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 Wed, May 16, 2012 at 02:40:22PM -0300, Marcelo Tosatti wrote: > On Wed, May 16, 2012 at 08:34:23PM +0300, Gleb Natapov wrote: > > On Wed, May 16, 2012 at 02:23:45PM -0300, Marcelo Tosatti wrote: > > > On Wed, May 16, 2012 at 08:21:55PM +0300, Gleb Natapov wrote: > > > > On Wed, May 16, 2012 at 02:04:27PM -0300, Marcelo Tosatti wrote: > > > > > On Wed, May 16, 2012 at 07:50:48PM +0300, Michael S. Tsirkin wrote: > > > > > > On Wed, May 16, 2012 at 07:32:06PM +0300, Gleb Natapov wrote: > > > > > > > On Wed, May 16, 2012 at 07:22:47PM +0300, Michael S. Tsirkin wrote: > > > > > > > > On Wed, May 16, 2012 at 12:49:40PM -0300, Marcelo Tosatti wrote: > > > > > > > > > > @@ -1245,9 +1306,20 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu) > > > > > > > > > > int vector = kvm_apic_has_interrupt(vcpu); > > > > > > > > > > struct kvm_lapic *apic = vcpu->arch.apic; > > > > > > > > > > > > > > > > > > > > - if (vector == -1) > > > > > > > > > > + /* Detect interrupt nesting and disable EOI optimization */ > > > > > > > > > > + if (pv_eoi_enabled(vcpu) && vector == -2) > > > > > > > > > > + pv_eoi_clr_pending(vcpu); > > > > > > > > > > + > > > > > > > > > > + if (vector < 0) > > > > > > > > > > > > > > > > > > With interrupt window exiting, the guest will exit: > > > > > > > > > > > > > > > > > > - as soon as it sets RFLAGS.IF=1 and there is any > > > > > > > > > interrupt pending in IRR. > > > > > > > > > - any new interrupt is set in IRR will kick vcpu > > > > > > > > > out of guest mode and recalculate interrupt-window-exiting. > > > > > > > > > > > > > > > > > > Doesnt this make this bit unnecessary ? > > > > > > > > > > > > > > > > Looks like we could cut it out. But I'm not sure how architectural it is > > > > > > > > that we exit on interrupt window. > > > > > > > We request exit on interrupt window only if there is pending irq that > > > > > > > can be delivered on a guest entry. > > > > > > > > > > > > Aha. If so what Marcelo proposed won't work I think: if we inject A then B > > > > > > which is lower priority, we need an exit on EOI, we can't inject > > > > > > immediately. > > > > > > > > > > Please describe the scenario clearly, i can't see the problem. > > > > > > > > During vcpu entry there are two IRRs set 100 and 200. 200 is injected, > > > > but irq window is not requested because 100 can't be injected, During > > > > EOI exit 100 is injected. > > > > > > interrupt window exiting is always requested if IRR is pending. Except > > > if NMI window is requested (which has higher priority). > > > > > This is where we enable irq window. We do it only if there is interrupt > > pending: > > if (kvm_cpu_has_interrupt(vcpu) || req_int_win) > > kvm_x86_ops->enable_irq_window(vcpu); > > > > kvm_cpu_has_interrupt() checks apic by calling kvm_apic_has_interrupt() > > > > > > kvm_apic_has_interrupt(): > > apic_update_ppr(apic); > > highest_irr = apic_find_highest_irr(apic); > > if ((highest_irr == -1) || > > ((highest_irr & 0xF0) <= apic_get_reg(apic, APIC_PROCPRI))) > > return -1; > > And above checks IRR priority, so we can have IRR set and do not enable > > irq window exit. > > Right, but then you cannot inject interrupt anyway so EOI is not > necessary. Instead TPR-below-threshold trap is set which handles > that case. No? > No. EOI clears ISR -> PROCPRI is recalculated -> pending interrupt is injected. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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