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Message-Id: <1582684862-10880-1-git-send-email-wanpengli@tencent.com>
Date: Wed, 26 Feb 2020 10:41:02 +0800
From: Wanpeng Li <kernellwp@...il.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>
Subject: [PATCH v3] KVM: LAPIC: Recalculate apic map in batch
From: Wanpeng Li <wanpengli@...cent.com>
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: Wanpeng Li <wanpengli@...cent.com>
---
v2 -> v3:
* move apic_map_dirty to kvm_arch
* add the suggestions from Paolo
v1 -> v2:
* add apic_map_dirty to kvm_lapic
* error condition in kvm_apic_set_state, do recalcuate unconditionally
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/lapic.c | 46 ++++++++++++++++++++++++++++++++---------
arch/x86/kvm/lapic.h | 1 +
arch/x86/kvm/x86.c | 1 +
4 files changed, 39 insertions(+), 10 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 40a0c0f..4380ed1 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -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;
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index afcd30d..de832aa 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -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)
@@ -1912,7 +1932,7 @@ 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;
@@ -2018,6 +2038,8 @@ 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);
@@ -2166,7 +2188,7 @@ 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;
}
}
@@ -2207,6 +2229,7 @@ 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);
@@ -2258,6 +2281,8 @@ 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);
}
/*
@@ -2479,17 +2504,18 @@ 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);
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index ec6fbfe..7581bc2 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -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,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 79bc995..d3802a2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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);
--
2.7.4
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