Messages in this thread Patch in this message | | | From | Wanpeng Li <> | Subject | [PATCH RESEND v3 1/5] KVM: LAPIC: Tune lapic_timer_advance_ns smoothly | Date | Fri, 6 Sep 2019 09:30:00 +0800 |
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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
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