From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@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 RESEND v3 1/5] KVM: LAPIC: Tune lapic_timer_advance_ns smoothly
Date: Fri, 6 Sep 2019 09:30:00 +0800 [thread overview]
Message-ID: <1567733404-7759-1-git-send-email-wanpengli@tencent.com> (raw)
From: Wanpeng Li <wanpengli@tencent.com>
Using a moving average based on per-vCPU lapic_timer_advance_ns to tune
smoothly, filter out drastic fluctuation which prevents this before,
let's assume it is 10000 cycles.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kvm/lapic.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e904ff0..2f4a48a 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -69,6 +69,7 @@
#define LAPIC_TIMER_ADVANCE_ADJUST_INIT 1000
/* step-by-step approximation to mitigate fluctuation */
#define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8
+#define LAPIC_TIMER_ADVANCE_FILTER 10000
static inline int apic_test_vector(int vec, void *bitmap)
{
@@ -1484,23 +1485,28 @@ static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,
s64 advance_expire_delta)
{
struct kvm_lapic *apic = vcpu->arch.apic;
- u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
- u64 ns;
+ u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns, ns;
+
+ if (abs(advance_expire_delta) > LAPIC_TIMER_ADVANCE_FILTER)
+ /* filter out drastic fluctuations */
+ return;
/* too early */
if (advance_expire_delta < 0) {
ns = -advance_expire_delta * 1000000ULL;
do_div(ns, vcpu->arch.virtual_tsc_khz);
- timer_advance_ns -= min((u32)ns,
- timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
+ timer_advance_ns -= ns;
} else {
/* too late */
ns = advance_expire_delta * 1000000ULL;
do_div(ns, vcpu->arch.virtual_tsc_khz);
- timer_advance_ns += min((u32)ns,
- timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
+ timer_advance_ns += ns;
}
+ timer_advance_ns = (apic->lapic_timer.timer_advance_ns *
+ (LAPIC_TIMER_ADVANCE_ADJUST_STEP - 1) + advance_expire_delta) /
+ LAPIC_TIMER_ADVANCE_ADJUST_STEP;
+
if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE)
apic->lapic_timer.timer_advance_adjust_done = true;
if (unlikely(timer_advance_ns > 5000)) {
--
2.7.4
next reply other threads:[~2019-09-06 1:30 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-06 1:30 Wanpeng Li [this message]
2019-09-06 1:30 ` [PATCH RESEND v3 2/5] KVM: LAPIC: Periodically revaluate to get conservative lapic_timer_advance_ns Wanpeng Li
2019-09-06 1:30 ` [PATCH RESEND 3/5] KVM: LAPIC: Micro optimize IPI latency Wanpeng Li
2019-09-06 1:30 ` [PATCH RESEND 4/5] KVM: VMX: Stop the preemption timer during vCPU reset Wanpeng Li
2019-09-06 1:30 ` [PATCH v2 5/5] KVM: hyperv: Fix Direct Synthetic timers assert an interrupt w/o lapic_in_kernel Wanpeng Li
2019-09-11 16:26 ` Paolo Bonzini
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