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([2001:b07:6468:f312:8c9d:1a6f:4730:367c]) by smtp.gmail.com with ESMTPSA id z6sm21332075wro.18.2019.11.11.13.59.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2019 13:59:08 -0800 (PST) Subject: Re: [PATCH 2/2] KVM: LAPIC: micro-optimize fixed mode ipi delivery To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel References: <1573283135-5502-1-git-send-email-wanpengli@tencent.com> <1573283135-5502-2-git-send-email-wanpengli@tencent.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <7a526814-c44e-c188-fba4-c6fb97b88b71@redhat.com> Date: Mon, 11 Nov 2019 22:59:08 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <1573283135-5502-2-git-send-email-wanpengli@tencent.com> Content-Language: en-US X-MC-Unique: TYUyoZsuMv2TyY88PXB0Tg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/11/19 08:05, Wanpeng Li wrote: > From: Wanpeng Li >=20 > After disabling mwait/halt/pause vmexits, RESCHEDULE_VECTOR and > CALL_FUNCTION_SINGLE_VECTOR etc IPI is one of the main remaining > cause of vmexits observed in product environment which can't be > optimized by PV IPIs. This patch is the follow-up on commit > 0e6d242eccdb (KVM: LAPIC: Micro optimize IPI latency), to optimize > redundancy logic before fixed mode ipi is delivered in the fast > path. >=20 > - broadcast handling needs to go slow path, so the delivery mode repair > can be delayed to before slow path. I agree with this part, but is the cost of the irq->shorthand check really measurable? Paolo > - self-IPI will not be intervened by hypervisor any more after APICv is > introduced and the boxes support APICv are popular now. In addition, > kvm_apic_map_get_dest_lapic() can handle the self-IPI, so there is no > need a shortcut for the non-APICv case. >=20 > Signed-off-by: Wanpeng Li > --- > arch/x86/kvm/irq_comm.c | 6 +++--- > arch/x86/kvm/lapic.c | 5 ----- > 2 files changed, 3 insertions(+), 8 deletions(-) >=20 > diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c > index 8ecd48d..aa88156 100644 > --- a/arch/x86/kvm/irq_comm.c > +++ b/arch/x86/kvm/irq_comm.c > @@ -52,15 +52,15 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct = kvm_lapic *src, > =09unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)]; > =09unsigned int dest_vcpus =3D 0; > =20 > +=09if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map)) > +=09=09return r; > + > =09if (irq->dest_mode =3D=3D 0 && irq->dest_id =3D=3D 0xff && > =09=09=09kvm_lowest_prio_delivery(irq)) { > =09=09printk(KERN_INFO "kvm: apic: phys broadcast and lowest prio\n"); > =09=09irq->delivery_mode =3D APIC_DM_FIXED; > =09} > =20 > -=09if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map)) > -=09=09return r; > - > =09memset(dest_vcpu_bitmap, 0, sizeof(dest_vcpu_bitmap)); > =20 > =09kvm_for_each_vcpu(i, vcpu, kvm) { > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index b29d00b..ea936fa 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -951,11 +951,6 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, = struct kvm_lapic *src, > =20 > =09*r =3D -1; > =20 > -=09if (irq->shorthand =3D=3D APIC_DEST_SELF) { > -=09=09*r =3D kvm_apic_set_irq(src->vcpu, irq, dest_map); > -=09=09return true; > -=09} > - > =09rcu_read_lock(); > =09map =3D rcu_dereference(kvm->arch.apic_map); > =20 >=20