KVM: LAPIC: Tune lapic_timer_advance_ns smoothly

Filter out drastic fluctuation and random fluctuation, remove
timer_advance_adjust_done altogether, the adjustment would be
continuous.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 8675458..3a3a685 100644 (file)
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -65,7 +65,9 @@
 #define APIC_BROADCAST                 0xFF
 #define X2APIC_BROADCAST               0xFFFFFFFFul
 
-#define LAPIC_TIMER_ADVANCE_ADJUST_DONE 100
+static bool lapic_timer_advance_dynamic __read_mostly;
+#define LAPIC_TIMER_ADVANCE_ADJUST_MIN 100
+#define LAPIC_TIMER_ADVANCE_ADJUST_MAX 5000
 #define LAPIC_TIMER_ADVANCE_ADJUST_INIT 1000
 /* step-by-step approximation to mitigate fluctuation */
 #define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8
@@ -1485,26 +1487,25 @@ static inline void adjust_lapic_timer_advance(struct kvm_vcpu *vcpu,
        u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
        u64 ns;
 
+       /* Do not adjust for tiny fluctuations or large random spikes. */
+       if (abs(advance_expire_delta) > LAPIC_TIMER_ADVANCE_ADJUST_MAX ||
+           abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_MIN)
+               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/LAPIC_TIMER_ADVANCE_ADJUST_STEP;
        } 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/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)) {
+       if (unlikely(timer_advance_ns > LAPIC_TIMER_ADVANCE_ADJUST_MAX))
                timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
-               apic->lapic_timer.timer_advance_adjust_done = false;
-       }
        apic->lapic_timer.timer_advance_ns = timer_advance_ns;
 }
 
@@ -1524,7 +1525,7 @@ static void __kvm_wait_lapic_expire(struct kvm_vcpu *vcpu)
        if (guest_tsc < tsc_deadline)
                __wait_lapic_expire(vcpu, tsc_deadline - guest_tsc);
 
-       if (unlikely(!apic->lapic_timer.timer_advance_adjust_done))
+       if (lapic_timer_advance_dynamic)
                adjust_lapic_timer_advance(vcpu, apic->lapic_timer.advance_expire_delta);
 }
 
@@ -2302,13 +2303,12 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns)
        apic->lapic_timer.timer.function = apic_timer_fn;
        if (timer_advance_ns == -1) {
                apic->lapic_timer.timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT;
-               apic->lapic_timer.timer_advance_adjust_done = false;
+               lapic_timer_advance_dynamic = true;
        } else {
                apic->lapic_timer.timer_advance_ns = timer_advance_ns;
-               apic->lapic_timer.timer_advance_adjust_done = true;
+               lapic_timer_advance_dynamic = false;
        }
 
-
        /*
         * APIC is created enabled. This will prevent kvm_lapic_set_base from
         * thinking that APIC state has changed.

diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 50053d2..2aad7e2 100644 (file)
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -35,7 +35,6 @@ struct kvm_timer {
        s64 advance_expire_delta;
        atomic_t pending;                       /* accumulated triggered timers */
        bool hv_timer_in_use;
-       bool timer_advance_adjust_done;
 };
 
 struct kvm_lapic {