From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David S. Ahern" Subject: Re: KVM: PIC: enhance IPI avoidance Date: Tue, 23 Sep 2008 21:05:44 -0600 Message-ID: <48D9AE88.7060603@cisco.com> References: <20080922165749.GA18733@dmt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Avi Kivity , kvm-devel To: Marcelo Tosatti Return-path: Received: from sj-iport-6.cisco.com ([171.71.176.117]:46554 "EHLO sj-iport-6.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751128AbYIXDFr (ORCPT ); Tue, 23 Sep 2008 23:05:47 -0400 In-Reply-To: <20080922165749.GA18733@dmt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: This patched worked very nicely for me -- about an 8% performance improvement for my workload. david Marcelo Tosatti wrote: > KVM: PIC: enhance IPI avoidance > > The PIC code makes little effort to avoid kvm_vcpu_kick(), resulting in > unnecessary guest exits in some conditions. > > For example, if the timer interrupt is routed through the IOAPIC, IRR > for IRQ 0 will get set but not cleared, since the APIC is handling the > acks. > > This means that everytime an interrupt < 16 is triggered, the priority > logic will find IRQ0 pending and send an IPI to vcpu0 (in case IRQ0 is > not masked, which is Linux's case). > > Introduce a new variable isr_ack to represent the IRQ's for which the > guest has been signalled / cleared the ISR. Use it to avoid more than > one IPI per trigger-ack cycle, in addition to the avoidance when ISR is > set in get_priority(). > > Signed-off-by: Marcelo Tosatti > > > Index: kvm/arch/x86/kvm/i8259.c > =================================================================== > --- kvm.orig/arch/x86/kvm/i8259.c > +++ kvm/arch/x86/kvm/i8259.c > @@ -33,6 +33,7 @@ > static void pic_clear_isr(struct kvm_kpic_state *s, int irq) > { > s->isr &= ~(1 << irq); > + s->isr_ack |= (1 << irq); > } > > /* > @@ -213,6 +214,7 @@ void kvm_pic_reset(struct kvm_kpic_state > s->irr = 0; > s->imr = 0; > s->isr = 0; > + s->isr_ack = 0xff; > s->priority_add = 0; > s->irq_base = 0; > s->read_reg_select = 0; > @@ -444,10 +446,14 @@ static void pic_irq_request(void *opaque > { > struct kvm *kvm = opaque; > struct kvm_vcpu *vcpu = kvm->vcpus[0]; > + struct kvm_pic *s = pic_irqchip(kvm); > + int irq = pic_get_irq(&s->pics[0]); > > - pic_irqchip(kvm)->output = level; > - if (vcpu) > + s->output = level; > + if (vcpu && level && (s->pics[0].isr_ack & (1 << irq))) { > + s->pics[0].isr_ack &= ~(1 << irq); > kvm_vcpu_kick(vcpu); > + } > } > > struct kvm_pic *kvm_create_pic(struct kvm *kvm) > Index: kvm/arch/x86/kvm/irq.h > =================================================================== > --- kvm.orig/arch/x86/kvm/irq.h > +++ kvm/arch/x86/kvm/irq.h > @@ -42,6 +42,7 @@ struct kvm_kpic_state { > u8 irr; /* interrupt request register */ > u8 imr; /* interrupt mask register */ > u8 isr; /* interrupt service register */ > + u8 isr_ack; /* interrupt ack detection */ > u8 priority_add; /* highest irq priority */ > u8 irq_base; > u8 read_reg_select; > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >