From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 83212C43613 for ; Fri, 21 Jun 2019 09:42:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 52F8421530 for ; Fri, 21 Jun 2019 09:42:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ZQofFxTw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726860AbfFUJmt (ORCPT ); Fri, 21 Jun 2019 05:42:49 -0400 Received: from mail-ot1-f68.google.com ([209.85.210.68]:46504 "EHLO mail-ot1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726780AbfFUJms (ORCPT ); Fri, 21 Jun 2019 05:42:48 -0400 Received: by mail-ot1-f68.google.com with SMTP id z23so5660911ote.13; Fri, 21 Jun 2019 02:42:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=Zt/rkE2uwb6CHB8DWB4fHAhRCcaDGCC18elm653yUDY=; b=ZQofFxTwBUPKH+zyHD0AH17wZUU0DCJaxZHMHZYckRylWbKITQHUZc9KhiI8mkcYWY 3bvUv8mw8+mFCIXpbTNA6C+g7ZrnY5ajfezudlhvz2hsrAMzWcaHUvmu76W3gCbxswca G0J2D8i6jaRXg4F6I+jENVcnoYM9lmsl3Ut3K9ZizmnqMnl/smd/XMJoFjw5sIWRVOcn xprZItGGQJ9N/uD9Ph+0PCG8L+2XMmp6cyO1WBeLI4vJfDJNhcR0U3EnZy+jsYwDZpMe A91Wi5Fm0JtW0/vUHmKe4RXc2eO0/h8vC32mxZnFPcSWcGaBkDSQZFgm+HGP4DvWRVds hssw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=Zt/rkE2uwb6CHB8DWB4fHAhRCcaDGCC18elm653yUDY=; b=CJenKUjpHE4oxg4FogP7aH5hlmVMZC0qHbIQPKo7JkulYJMHN4pQIXbZSJAdujMmF3 9gCAZUWHedRJBvtUPqW2YS6mLgAAdUpBD8wPSrpi/P85nEeWm8LZTVipFnJNAVsO1j3e QmWo+GOJb069cSOhD5kXEREaKS8g/x8aSZzF3Ou00yU3wK3UnZufwxm4oBpGV15u1Xlu ljVdOp6CZ3TpUSinSJtESnm+yJZnmBolqqPiNXVX/x5uqMLgEhPLrzginFruiJS8HpbG LON9tRj12Gcv11MU6Gw60r8Un3wQPxlIH2qc/Jcjzs93GQjOzCTHkNC6bt7fWYTQiw7J +p9g== X-Gm-Message-State: APjAAAVKdq2eNScHlUywyGNIkGSXO8FwWtti8KOiGV5EeKjygXRxJBs/ VbJiBmYo6cSoWgaazaw1wBQchowrv+97UpjsFTvZCA== X-Google-Smtp-Source: APXvYqzXaxnHnbrDiK893TTngEMYU6AznBNF5SGeiHoNi5DIMU1hATKzIzNQ81kaD16ArmnAJxWZYecejazZWPirLKI= X-Received: by 2002:a9d:62c4:: with SMTP id z4mr7101354otk.56.1561110167615; Fri, 21 Jun 2019 02:42:47 -0700 (PDT) MIME-Version: 1.0 References: <1560474949-20497-1-git-send-email-wanpengli@tencent.com> <1560474949-20497-2-git-send-email-wanpengli@tencent.com> In-Reply-To: <1560474949-20497-2-git-send-email-wanpengli@tencent.com> From: Wanpeng Li Date: Fri, 21 Jun 2019 17:44:00 +0800 Message-ID: Subject: Re: [PATCH v4 1/2] KVM: LAPIC: Optimize timer latency consider world switch time To: LKML , kvm Cc: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Sean Christopherson Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org ping, On Fri, 14 Jun 2019 at 09:15, Wanpeng Li wrote: > > From: Wanpeng Li > > Advance lapic timer tries to hidden the hypervisor overhead between the > host emulated timer fires and the guest awares the timer is fired. Howeve= r, > even though after more sustaining optimizations, kvm-unit-tests/tscdeadli= ne_latency > still awares ~1000 cycles latency since we lost the time between the end = of > wait_lapic_expire and the guest awares the timer is fired. There are > codes between the end of wait_lapic_expire and the world switch, furtherm= ore, > the world switch itself also has overhead. Actually the guest_tsc is equa= l > to the target deadline time in wait_lapic_expire is too late, guest will > aware the latency between the end of wait_lapic_expire() and after vmentr= y > to the guest. This patch takes this time into consideration. > > The vmentry_advance_ns module parameter is conservative 25ns by default(t= hanks > to Radim's kvm-unit-tests/vmentry_latency.flat), it can be tuned/reworked= in > the future. > > Cc: Paolo Bonzini > Cc: Radim Kr=C4=8Dm=C3=A1=C5=99 > Cc: Sean Christopherson > Signed-off-by: Wanpeng Li > --- > v3 -> v4: > * default value is 25ns > * compute vmentry_advance_cycles in kvm_set_tsc_khz() path > v2 -> v3: > * read-only module parameter > * get_vmentry_advance_cycles() not inline > v1 -> v2: > * rename get_vmentry_advance_delta to get_vmentry_advance_cycles > * cache vmentry_advance_cycles by setting param bit 0 > * add param max limit > > arch/x86/kvm/lapic.c | 21 ++++++++++++++++++--- > arch/x86/kvm/lapic.h | 2 ++ > arch/x86/kvm/vmx/vmx.c | 3 ++- > arch/x86/kvm/x86.c | 12 ++++++++++-- > arch/x86/kvm/x86.h | 2 ++ > 5 files changed, 34 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index e82a18c..e92e4e5 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1528,6 +1528,19 @@ static inline void adjust_lapic_timer_advance(stru= ct kvm_vcpu *vcpu, > apic->lapic_timer.timer_advance_ns =3D timer_advance_ns; > } > > +u64 compute_vmentry_advance_cycles(struct kvm_vcpu *vcpu) > +{ > + u64 cycles; > + struct kvm_lapic *apic =3D vcpu->arch.apic; > + > + cycles =3D vmentry_advance_ns * vcpu->arch.virtual_tsc_khz; > + do_div(cycles, 1000000); > + > + apic->lapic_timer.vmentry_advance_cycles =3D cycles; > + > + return cycles; > +} > + > void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) > { > struct kvm_lapic *apic =3D vcpu->arch.apic; > @@ -1541,7 +1554,8 @@ void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu) > > tsc_deadline =3D apic->lapic_timer.expired_tscdeadline; > apic->lapic_timer.expired_tscdeadline =3D 0; > - guest_tsc =3D kvm_read_l1_tsc(vcpu, rdtsc()); > + guest_tsc =3D kvm_read_l1_tsc(vcpu, rdtsc()) + > + apic->lapic_timer.vmentry_advance_cycles; > apic->lapic_timer.advance_expire_delta =3D guest_tsc - tsc_deadli= ne; > > if (guest_tsc < tsc_deadline) > @@ -1569,7 +1583,8 @@ static void start_sw_tscdeadline(struct kvm_lapic *= apic) > local_irq_save(flags); > > now =3D ktime_get(); > - guest_tsc =3D kvm_read_l1_tsc(vcpu, rdtsc()); > + guest_tsc =3D kvm_read_l1_tsc(vcpu, rdtsc()) + > + apic->lapic_timer.vmentry_advance_cycles; > > ns =3D (tscdeadline - guest_tsc) * 1000000ULL; > do_div(ns, this_tsc_khz); > @@ -2326,7 +2341,7 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int tim= er_advance_ns) > apic->lapic_timer.timer_advance_ns =3D timer_advance_ns; > apic->lapic_timer.timer_advance_adjust_done =3D true; > } > - > + apic->lapic_timer.vmentry_advance_cycles =3D 0; > > /* > * APIC is created enabled. This will prevent kvm_lapic_set_base = from > diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h > index 3674717..7c38950 100644 > --- a/arch/x86/kvm/lapic.h > +++ b/arch/x86/kvm/lapic.h > @@ -33,6 +33,7 @@ struct kvm_timer { > u64 expired_tscdeadline; > u32 timer_advance_ns; > s64 advance_expire_delta; > + u64 vmentry_advance_cycles; > atomic_t pending; /* accumulated triggered = timers */ > bool hv_timer_in_use; > bool timer_advance_adjust_done; > @@ -226,6 +227,7 @@ static inline int kvm_lapic_latched_init(struct kvm_v= cpu *vcpu) > bool kvm_apic_pending_eoi(struct kvm_vcpu *vcpu, int vector); > > void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu); > +u64 compute_vmentry_advance_cycles(struct kvm_vcpu *vcpu); > > bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq = *irq, > struct kvm_vcpu **dest_vcpu); > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 8fbea03..dc81c78 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -7064,7 +7064,8 @@ static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, = u64 guest_deadline_tsc, > > vmx =3D to_vmx(vcpu); > tscl =3D rdtsc(); > - guest_tscl =3D kvm_read_l1_tsc(vcpu, tscl); > + guest_tscl =3D kvm_read_l1_tsc(vcpu, tscl) + > + vcpu->arch.apic->lapic_timer.vmentry_advance_cycles; > delta_tsc =3D max(guest_deadline_tsc, guest_tscl) - guest_tscl; > lapic_timer_advance_cycles =3D nsec_to_cycles(vcpu, > ktimer->timer_advance= _ns); > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 0a05a4e..5e79b6c 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -145,6 +145,12 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IW= USR); > static int __read_mostly lapic_timer_advance_ns =3D -1; > module_param(lapic_timer_advance_ns, int, S_IRUGO | S_IWUSR); > > +/* > + * lapic timer vmentry advance (tscdeadline mode only) in nanoseconds. > + */ > +u32 __read_mostly vmentry_advance_ns =3D 25; > +module_param(vmentry_advance_ns, uint, S_IRUGO); > + > static bool __read_mostly vector_hashing =3D true; > module_param(vector_hashing, bool, S_IRUGO); > > @@ -1592,6 +1598,8 @@ static int kvm_set_tsc_khz(struct kvm_vcpu *vcpu, u= 32 user_tsc_khz) > kvm_get_time_scale(user_tsc_khz * 1000LL, NSEC_PER_SEC, > &vcpu->arch.virtual_tsc_shift, > &vcpu->arch.virtual_tsc_mult); > + if (user_tsc_khz !=3D vcpu->arch.virtual_tsc_khz) > + compute_vmentry_advance_cycles(vcpu); > vcpu->arch.virtual_tsc_khz =3D user_tsc_khz; > > /* > @@ -9134,8 +9142,6 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) > } > vcpu->arch.pio_data =3D page_address(page); > > - kvm_set_tsc_khz(vcpu, max_tsc_khz); > - > r =3D kvm_mmu_create(vcpu); > if (r < 0) > goto fail_free_pio_data; > @@ -9148,6 +9154,8 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu) > } else > static_key_slow_inc(&kvm_no_apic_vcpu); > > + kvm_set_tsc_khz(vcpu, max_tsc_khz); > + > vcpu->arch.mce_banks =3D kzalloc(KVM_MAX_MCE_BANKS * sizeof(u64) = * 4, > GFP_KERNEL_ACCOUNT); > if (!vcpu->arch.mce_banks) { > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h > index e08a128..9998989 100644 > --- a/arch/x86/kvm/x86.h > +++ b/arch/x86/kvm/x86.h > @@ -299,6 +299,8 @@ extern u64 kvm_supported_xcr0(void); > > extern unsigned int min_timer_period_us; > > +extern unsigned int vmentry_advance_ns; > + > extern bool enable_vmware_backdoor; > > extern struct static_key kvm_no_apic_vcpu; > -- > 2.7.4 >