From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: [PATCH v2 6/9] KVM: LAPIC: Reduce world switch latency caused by timer_advance_ns
Date: Thu, 10 Sep 2020 17:50:41 +0800 [thread overview]
Message-ID: <1599731444-3525-7-git-send-email-wanpengli@tencent.com> (raw)
In-Reply-To: <1599731444-3525-1-git-send-email-wanpengli@tencent.com>
From: Wanpeng Li <wanpengli@tencent.com>
All the checks in lapic_timer_int_injected(), __kvm_wait_lapic_expire(), and
these function calls waste cpu cycles when the timer mode is not tscdeadline.
We can observe ~1.3% world switch time overhead by kvm-unit-tests/vmexit.flat
vmcall testing on AMD server. This patch reduces the world switch latency
caused by timer_advance_ns feature when the timer mode is not tscdeadline by
simpling move the check against apic->lapic_timer.expired_tscdeadline much
earlier.
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kvm/lapic.c | 11 +++++------
arch/x86/kvm/svm/svm.c | 4 +---
arch/x86/kvm/vmx/vmx.c | 4 +---
3 files changed, 7 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 3b32d3b..51ed4f0 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1582,9 +1582,6 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
struct kvm_lapic *apic = vcpu->arch.apic;
u64 guest_tsc, tsc_deadline;
- if (apic->lapic_timer.expired_tscdeadline == 0)
- return;
-
tsc_deadline = apic->lapic_timer.expired_tscdeadline;
apic->lapic_timer.expired_tscdeadline = 0;
guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc());
@@ -1599,7 +1596,10 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
void kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
{
- if (lapic_timer_int_injected(vcpu))
+ if (lapic_in_kernel(vcpu) &&
+ vcpu->arch.apic->lapic_timer.expired_tscdeadline &&
+ vcpu->arch.apic->lapic_timer.timer_advance_ns &&
+ lapic_timer_int_injected(vcpu))
__kvm_wait_lapic_expire(vcpu);
}
EXPORT_SYMBOL_GPL(kvm_wait_lapic_expire);
@@ -1635,8 +1635,7 @@ static void apic_timer_expired(struct kvm_lapic *apic, bool from_timer_fn)
}
if (kvm_use_posted_timer_interrupt(apic->vcpu)) {
- if (apic->lapic_timer.timer_advance_ns)
- __kvm_wait_lapic_expire(vcpu);
+ kvm_wait_lapic_expire(vcpu);
kvm_apic_inject_pending_timer_irqs(apic);
return;
}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 0194336..19e622a 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3456,9 +3456,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
clgi();
kvm_load_guest_xsave_state(vcpu);
- if (lapic_in_kernel(vcpu) &&
- vcpu->arch.apic->lapic_timer.timer_advance_ns)
- kvm_wait_lapic_expire(vcpu);
+ kvm_wait_lapic_expire(vcpu);
/*
* If this vCPU has touched SPEC_CTRL, restore the guest's value if
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a544351..d6e1656 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6800,9 +6800,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
if (enable_preemption_timer)
vmx_update_hv_timer(vcpu);
- if (lapic_in_kernel(vcpu) &&
- vcpu->arch.apic->lapic_timer.timer_advance_ns)
- kvm_wait_lapic_expire(vcpu);
+ kvm_wait_lapic_expire(vcpu);
/*
* If this vCPU has touched SPEC_CTRL, restore the guest's value if
--
2.7.4
next prev parent reply other threads:[~2020-09-10 9:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-10 9:50 [PATCH v2 0/9] KVM: collect sporadic patches Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 1/9] KVM: LAPIC: Return 0 when getting the tscdeadline timer if the lapic is hw disabled Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 2/9] KVM: LAPIC: Guarantee the timer is in tsc-deadline mode when setting Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 3/9] KVM: LAPIC: Fix updating DFR missing apic map recalculation Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 4/9] KVM: VMX: Don't freeze guest when event delivery causes an APIC-access exit Wanpeng Li
2020-09-29 21:42 ` Jim Mattson
2020-09-10 9:50 ` [PATCH v2 5/9] KVM: LAPIC: Narrow down the kick target vCPU Wanpeng Li
2020-09-12 6:46 ` Paolo Bonzini
2020-09-10 9:50 ` Wanpeng Li [this message]
2020-09-10 9:50 ` [PATCH v2 7/9] KVM: SVM: Get rid of handle_fastpath_set_msr_irqoff() Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 8/9] KVM: SVM: Move svm_complete_interrupts() into svm_vcpu_run() Wanpeng Li
2020-09-10 9:50 ` [PATCH v2 9/9] KVM: SVM: Reenable handle_fastpath_set_msr_irqoff() after complete_interrupts() Wanpeng Li
2020-09-12 6:47 ` [PATCH v2 0/9] KVM: collect sporadic patches Paolo Bonzini
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1599731444-3525-7-git-send-email-wanpengli@tencent.com \
--to=kernellwp@gmail.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=sean.j.christopherson@intel.com \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.