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KVM: LAPIC: Tune lapic_timer_advance_ns smoothly

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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>
This commit is contained in:
Wanpeng Li
2019-09-17 16:16:26 +08:00
committed by Paolo Bonzini
parent bf653b78f9
commit d0f5a86a34
2 changed files with 14 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

28
arch/x86/kvm/lapic.c
View File

@@ -65,7 +65,9 @@
#define APIC_BROADCAST 0xFF #define APIC_BROADCAST 0xFF
#define X2APIC_BROADCAST 0xFFFFFFFFul #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 #define LAPIC_TIMER_ADVANCE_ADJUST_INIT 1000
/* step-by-step approximation to mitigate fluctuation */ /* step-by-step approximation to mitigate fluctuation */
#define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8 #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; u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
u64 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 */ /* too early */
if (advance_expire_delta < 0) { if (advance_expire_delta < 0) {
ns = -advance_expire_delta * 1000000ULL; ns = -advance_expire_delta * 1000000ULL;
do_div(ns, vcpu->arch.virtual_tsc_khz); do_div(ns, vcpu->arch.virtual_tsc_khz);
timer_advance_ns -= min((u32)ns, timer_advance_ns -= ns/LAPIC_TIMER_ADVANCE_ADJUST_STEP;
timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
} else { } else {
/* too late */ /* too late */
ns = advance_expire_delta * 1000000ULL; ns = advance_expire_delta * 1000000ULL;
do_div(ns, vcpu->arch.virtual_tsc_khz); do_div(ns, vcpu->arch.virtual_tsc_khz);
timer_advance_ns += min((u32)ns, timer_advance_ns += ns/LAPIC_TIMER_ADVANCE_ADJUST_STEP;
timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP);
} }
if (abs(advance_expire_delta) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) if (unlikely(timer_advance_ns > LAPIC_TIMER_ADVANCE_ADJUST_MAX))
apic->lapic_timer.timer_advance_adjust_done = true;
if (unlikely(timer_advance_ns > 5000)) {
timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT; 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; 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) if (guest_tsc < tsc_deadline)
__wait_lapic_expire(vcpu, tsc_deadline - guest_tsc); __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); 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; apic->lapic_timer.timer.function = apic_timer_fn;
if (timer_advance_ns == -1) { if (timer_advance_ns == -1) {
apic->lapic_timer.timer_advance_ns = LAPIC_TIMER_ADVANCE_ADJUST_INIT; 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 { } else {
apic->lapic_timer.timer_advance_ns = timer_advance_ns; 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 * APIC is created enabled. This will prevent kvm_lapic_set_base from
* thinking that APIC state has changed. * thinking that APIC state has changed.

1
arch/x86/kvm/lapic.h
View File

@@ -35,7 +35,6 @@ struct kvm_timer {
s64 advance_expire_delta; s64 advance_expire_delta;
atomic_t pending; /* accumulated triggered timers */ atomic_t pending; /* accumulated triggered timers */
bool hv_timer_in_use; bool hv_timer_in_use;
bool timer_advance_adjust_done;
}; };
struct kvm_lapic { struct kvm_lapic {