Commit 4abaffce authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
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KVM: LAPIC: Recalculate apic map in batch



In the vCPU reset and set APIC_BASE MSR path, the apic map will be recalculated
several times, each time it will consume 10+ us observed by ftrace in my
non-overcommit environment since the expensive memory allocate/mutex/rcu etc
operations. This patch optimizes it by recaluating apic map in batch, I hope
this can benefit the serverless scenario which can frequently create/destroy
VMs.

Before patch:

kvm_lapic_reset  ~27us

After patch:

kvm_lapic_reset  ~14us

Observed by ftrace, improve ~48%.
Signed-off-by: default avatarWanpeng Li <wanpengli@tencent.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 49f933d4
......@@ -920,6 +920,7 @@ struct kvm_arch {
atomic_t vapics_in_nmi_mode;
struct mutex apic_map_lock;
struct kvm_apic_map *apic_map;
bool apic_map_dirty;
bool apic_access_page_done;
unsigned long apicv_inhibit_reasons;
......
......@@ -164,14 +164,28 @@ static void kvm_apic_map_free(struct rcu_head *rcu)
kvfree(map);
}
static void recalculate_apic_map(struct kvm *kvm)
void kvm_recalculate_apic_map(struct kvm *kvm)
{
struct kvm_apic_map *new, *old = NULL;
struct kvm_vcpu *vcpu;
int i;
u32 max_id = 255; /* enough space for any xAPIC ID */
if (!kvm->arch.apic_map_dirty) {
/*
* Read kvm->arch.apic_map_dirty before
* kvm->arch.apic_map
*/
smp_rmb();
return;
}
mutex_lock(&kvm->arch.apic_map_lock);
if (!kvm->arch.apic_map_dirty) {
/* Someone else has updated the map. */
mutex_unlock(&kvm->arch.apic_map_lock);
return;
}
kvm_for_each_vcpu(i, vcpu, kvm)
if (kvm_apic_present(vcpu))
......@@ -236,6 +250,12 @@ static void recalculate_apic_map(struct kvm *kvm)
old = rcu_dereference_protected(kvm->arch.apic_map,
lockdep_is_held(&kvm->arch.apic_map_lock));
rcu_assign_pointer(kvm->arch.apic_map, new);
/*
* Write kvm->arch.apic_map before
* clearing apic->apic_map_dirty
*/
smp_wmb();
kvm->arch.apic_map_dirty = false;
mutex_unlock(&kvm->arch.apic_map_lock);
if (old)
......@@ -257,20 +277,20 @@ static inline void apic_set_spiv(struct kvm_lapic *apic, u32 val)
else
static_key_slow_inc(&apic_sw_disabled.key);
recalculate_apic_map(apic->vcpu->kvm);
apic->vcpu->kvm->arch.apic_map_dirty = true;
}
}
static inline void kvm_apic_set_xapic_id(struct kvm_lapic *apic, u8 id)
{
kvm_lapic_set_reg(apic, APIC_ID, id << 24);
recalculate_apic_map(apic->vcpu->kvm);
apic->vcpu->kvm->arch.apic_map_dirty = true;
}
static inline void kvm_apic_set_ldr(struct kvm_lapic *apic, u32 id)
{
kvm_lapic_set_reg(apic, APIC_LDR, id);
recalculate_apic_map(apic->vcpu->kvm);
apic->vcpu->kvm->arch.apic_map_dirty = true;
}
static inline u32 kvm_apic_calc_x2apic_ldr(u32 id)
......@@ -286,7 +306,7 @@ static inline void kvm_apic_set_x2apic_id(struct kvm_lapic *apic, u32 id)
kvm_lapic_set_reg(apic, APIC_ID, id);
kvm_lapic_set_reg(apic, APIC_LDR, ldr);
recalculate_apic_map(apic->vcpu->kvm);
apic->vcpu->kvm->arch.apic_map_dirty = true;
}
static inline int apic_lvt_enabled(struct kvm_lapic *apic, int lvt_type)
......@@ -1906,7 +1926,7 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
case APIC_DFR:
if (!apic_x2apic_mode(apic)) {
kvm_lapic_set_reg(apic, APIC_DFR, val | 0x0FFFFFFF);
recalculate_apic_map(apic->vcpu->kvm);
apic->vcpu->kvm->arch.apic_map_dirty = true;
} else
ret = 1;
break;
......@@ -2012,6 +2032,8 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
break;
}
kvm_recalculate_apic_map(apic->vcpu->kvm);
return ret;
}
EXPORT_SYMBOL_GPL(kvm_lapic_reg_write);
......@@ -2160,7 +2182,7 @@ void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value)
static_key_slow_dec_deferred(&apic_hw_disabled);
} else {
static_key_slow_inc(&apic_hw_disabled.key);
recalculate_apic_map(vcpu->kvm);
vcpu->kvm->arch.apic_map_dirty = true;
}
}
......@@ -2201,6 +2223,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
if (!apic)
return;
vcpu->kvm->arch.apic_map_dirty = false;
/* Stop the timer in case it's a reset to an active apic */
hrtimer_cancel(&apic->lapic_timer.timer);
......@@ -2252,6 +2275,8 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
vcpu->arch.apic_arb_prio = 0;
vcpu->arch.apic_attention = 0;
kvm_recalculate_apic_map(vcpu->kvm);
}
/*
......@@ -2473,17 +2498,18 @@ int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)
struct kvm_lapic *apic = vcpu->arch.apic;
int r;
kvm_lapic_set_base(vcpu, vcpu->arch.apic_base);
/* set SPIV separately to get count of SW disabled APICs right */
apic_set_spiv(apic, *((u32 *)(s->regs + APIC_SPIV)));
r = kvm_apic_state_fixup(vcpu, s, true);
if (r)
if (r) {
kvm_recalculate_apic_map(vcpu->kvm);
return r;
}
memcpy(vcpu->arch.apic->regs, s->regs, sizeof(*s));
recalculate_apic_map(vcpu->kvm);
kvm_recalculate_apic_map(vcpu->kvm);
kvm_apic_set_version(vcpu);
apic_update_ppr(apic);
......
......@@ -78,6 +78,7 @@ void kvm_lapic_set_tpr(struct kvm_vcpu *vcpu, unsigned long cr8);
void kvm_lapic_set_eoi(struct kvm_vcpu *vcpu);
void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value);
u64 kvm_lapic_get_base(struct kvm_vcpu *vcpu);
void kvm_recalculate_apic_map(struct kvm *kvm);
void kvm_apic_set_version(struct kvm_vcpu *vcpu);
int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val);
int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
......
......@@ -350,6 +350,7 @@ int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
}
kvm_lapic_set_base(vcpu, msr_info->data);
kvm_recalculate_apic_map(vcpu->kvm);
return 0;
}
EXPORT_SYMBOL_GPL(kvm_set_apic_base);
......
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