From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: KVM: PIC: enhance IPI avoidance Date: Mon, 22 Sep 2008 13:57:49 -0300 Message-ID: <20080922165749.GA18733@dmt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm-devel To: Avi Kivity Return-path: Received: from mx2.redhat.com ([66.187.237.31]:57477 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751382AbYIVQ7H (ORCPT ); Mon, 22 Sep 2008 12:59:07 -0400 Content-Disposition: inline Sender: kvm-owner@vger.kernel.org List-ID: 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;