Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758877Ab2EUSog (ORCPT ); Mon, 21 May 2012 14:44:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:31320 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750842Ab2EUSod (ORCPT ); Mon, 21 May 2012 14:44:33 -0400 Date: Mon, 21 May 2012 21:44:28 +0300 From: "Michael S. Tsirkin" To: kvm@vger.kernel.org Cc: Avi Kivity , Marcelo Tosatti , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] kvm: optimize ISR lookups Message-ID: <20120521184352.GA14463@redhat.com> References: <20120521163727.GA13337@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120521163727.GA13337@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6054 Lines: 183 On Mon, May 21, 2012 at 07:37:27PM +0300, Michael S. Tsirkin wrote: > We perform ISR lookups twice: during interrupt > injection and on EOI. Typical workloads only have > a single bit set there. So we can avoid ISR scans by > 1. counting bits as we set/clear them in ISR > 2. if count is 1, caching the vector number > 3. if count != 1, invalidating the cache > > The real purpose of this is enabling PV EOI > which needs to quickly validate the vector. > But non PV guests also benefit. > > Signed-off-by: Michael S. Tsirkin BTW host to guest netperf result (which is 100% CPU bound) seems to increase pretty drastically: before TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.104 (11.0.0.104) port 0 AF_INET Recv Send Send Utilization Service Demand Socket Socket Message Elapsed Send Recv Send Recv Size Size Size Time Throughput local remote local remote bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB 87380 16384 16384 10.01 7905.79 11.26 99.50 2.801 1.031 after TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.104 (11.0.0.104) port 0 AF_INET Recv Send Send Utilization Service Demand Socket Socket Message Elapsed Send Recv Send Recv Size Size Size Time Throughput local remote local remote bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB 87380 16384 16384 10.01 8826.59 11.36 99.20 2.531 0.921 > --- > arch/x86/kvm/lapic.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++- > arch/x86/kvm/lapic.h | 2 + > 2 files changed, 51 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 93c1574..232950a 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -107,6 +107,16 @@ static inline void apic_clear_vector(int vec, void *bitmap) > clear_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > } > > +static inline int __apic_test_and_set_vector(int vec, void *bitmap) > +{ > + return __test_and_set_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > +} > + > +static inline int __apic_test_and_clear_vector(int vec, void *bitmap) > +{ > + return __test_and_clear_bit(VEC_POS(vec), (bitmap) + REG_POS(vec)); > +} > + > static inline int apic_hw_enabled(struct kvm_lapic *apic) > { > return (apic)->vcpu->arch.apic_base & MSR_IA32_APICBASE_ENABLE; > @@ -210,6 +220,16 @@ static int find_highest_vector(void *bitmap) > return fls(word[word_offset << 2]) - 1 + (word_offset << 5); > } > > +static u8 count_vectors(void *bitmap) > +{ > + u32 *word = bitmap; > + int word_offset; > + u8 count = 0; > + for (word_offset = 0; word_offset < MAX_APIC_VECTOR >> 5; ++word_offset) > + count += hweight32(word[word_offset << 2]); > + return count; > +} > + > static inline int apic_test_and_set_irr(int vec, struct kvm_lapic *apic) > { > apic->irr_pending = true; > @@ -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); > + 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); > + apic->isr_cache = -1; > +} > + > int kvm_lapic_find_highest_irr(struct kvm_vcpu *vcpu) > { > struct kvm_lapic *apic = vcpu->arch.apic; > @@ -273,6 +312,10 @@ int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq) > static inline int apic_find_highest_isr(struct kvm_lapic *apic) > { > int result; > + if (!apic->isr_count) > + return -1; > + if (likely(apic->isr_cache != -1)) > + return apic->isr_cache; > > result = find_highest_vector(apic->regs + APIC_ISR); > ASSERT(result == -1 || result >= 16); > @@ -492,7 +535,7 @@ static void apic_set_eoi(struct kvm_lapic *apic) > if (vector == -1) > return; > > - apic_clear_vector(vector, apic->regs + APIC_ISR); > + apic_clear_isr(vector, apic); > apic_update_ppr(apic); > > if (!(apic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI) && > @@ -1081,6 +1124,8 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu) > apic_set_reg(apic, APIC_TMR + 0x10 * i, 0); > } > apic->irr_pending = false; > + apic->isr_count = 0; > + apic->isr_cache = -1; > update_divide_count(apic); > atomic_set(&apic->lapic_timer.pending, 0); > if (kvm_vcpu_is_bsp(vcpu)) > @@ -1248,7 +1293,7 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu) > if (vector == -1) > return -1; > > - apic_set_vector(vector, apic->regs + APIC_ISR); > + apic_set_isr(vector, apic); > apic_update_ppr(apic); > apic_clear_irr(vector, apic); > return vector; > @@ -1267,6 +1312,8 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu) > update_divide_count(apic); > start_apic_timer(apic); > apic->irr_pending = true; > + apic->isr_count = count_vectors(apic->regs + APIC_ISR); > + apic->isr_cache = -1; > kvm_make_request(KVM_REQ_EVENT, vcpu); > } > > diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h > index 6f4ce25..9f8deff 100644 > --- a/arch/x86/kvm/lapic.h > +++ b/arch/x86/kvm/lapic.h > @@ -13,6 +13,8 @@ struct kvm_lapic { > u32 divide_count; > struct kvm_vcpu *vcpu; > bool irr_pending; > + s16 isr_count; > + int isr_cache; > void *regs; > gpa_t vapic_addr; > struct page *vapic_page; > -- > MST -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/