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Commit d0f5a86a authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
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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: default avatarWanpeng Li <wanpengli@tencent.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent bf653b78

arch/x86/kvm/lapic.c

+14 −14
Original line number Diff line number Diff line
@@ -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.

arch/x86/kvm/lapic.h

+0 −1
Original line number Diff line number Diff line
@@ -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 {